Meet the disease at its first stage. Persius (50 A.D.)
The average detectorist can benefit from a few periodic maintenance techniques employed by professionals in caring for their machines. There aren't many steps in this maintenance procedure, because detector manufacturers have demonstrated remarkable foresight in designing sensitive, yet durable equipment.
Almost military in ruggedness and reliability, good detectors hold up well under all manner of environmental conditions, including extreme cold and heat, blowing sand and snow, rain, spray, and general thumping and tossing about. A well made detector is a remarkable piece of electronic equipment that more than deserves the little bit of pampering needed to extend its life.
A small amount of care at the onset of a defect can stop it from escalating into something expensive or even fatal to your machine.
To begin with, get into the habit of keeping your detector clean. Grit, sand, and liquids have a nasty way of sneaking into its entrails and causing all manner of damage, some of it not immediately noticeable. Yet its a simple matter to get rid of most of these malignant intruders.
After each use, wipe the detector off with a clean, damp cloth. If necessary, use a mild detergent solution, sparingly, then remove deposits with a cloth dampened with fresh water. Dry with a lint-free cloth or paper towel. Keep water away from the control housing, although that, too, should be cleaned lightly with a damp cloth. Rinse the search coil with a garden hose or under a faucet, and dry it with an absorbent towel. After a beach hunt, separate the sections of the shaft, clean out and dry the interiors, then re-assemble them.
Every so often, not necessarily after each use, remove the protective skid plate (i.e., coil cover) and, if necessary, clean and dry its interior and the bottom of the search coil. If you didn't do so when you first bought the detector, you might consider the desirability of marking the inside of the skid plate or the bottom of the search coil with your initials or some other personal code in case of theft. Most thieves are not technically competent and, more likely than not, would be unaware the cover is removable. Use a laundry marker; the marking will not show through the cover.
Some THers have suggested the additional precaution of making the mark with light colored or invisible fluorescent ink rather than with a marker, so that it can be seen only by exposure to black (i.e., ultra-violet) light. Although it seems like a good idea, I don't recommend it. Most fluorescent inks have a metal base that may cause problems during detection.
Although a coil cover is nothing but a piece of plastic that can cost $10 or more, the expense is warranted. It's foolish to try to save money by not buying one, as it acts as a sacrificial barrier to protect the expensive coil that it covers, and it lasts a surprisingly long time considering the action it sees. The coil itself looks almost brand new when the cover finally gives up the ghost, which might be after half a dozen or more brutal years of detecting.
If several inspections, at various intervals, show the coil cover does not fit tightly, as evidenced by accumulations of liquid or metallic particles that might affect detection, seal the joint where the cover and coil mate with a thin bead of some sort of caulking material. Vinyl adhesive (Polyseamseal or equivalent) normally used for general sealing around tubs and bathroom fixtures works well. The white color matches that of most skid plates; it dries rapidly and cleans up with soap and water; it is waterproof and stays in place after it dries, yet can be readily removed when necessary and, most important, contains nothing that will interfere with detection.
The search coil needs no other maintenance, but you might want to feed the rubber washers in the coil positioning mechanism once in a while with an application of silicone liquid to keep them soft and resilient. This is not lubrication. The washers are friction clutch devices and must not be lubricated. (For that matter, don't lubricate any portion of the detector; a lubricant can degrade its operation, possibly even stop it from working permanently if it gets on switch contacts or inside electrical sockets.)
If you use spray rather than liquid, don't spray the silicone at the machine. Instead, remove the washers, apply the liquid to a lint-free cloth away from the detector, wipe the silicone all over the washers, and allow it to penetrate the rubber for a few minutes. Then remove any residue with a clean paper towel and reinstall the washers.
Also, while working with them, inspect the washers for nicks or other damage that might require replacement, and check the mounting area on the coil housing for dirt. Clean as required. This treatment can also be used on rubber handles, grips, and other rubber or leather parts of the detector. Use silicone spray in a well-ventilated area away from open flames.
Remove non-rechargeable batteries from their holders and check for signs of corrosion or leakage. Any such indication requires their immediate replacement. Don't try to save any of the cells - replace the entire set. It's a lot cheaper than repairing a damaged detector. Clean out any corrosion before installing the new cells, then operate the detector to determine that it is working properly. Ensure that rechargeable batteries are in proper condition; if low, allow them to discharge, then recharge them for operational readiness.
Verify that the connector on the coil cable is securely fastened to its mate on the control housing. Also ensure that the cable is wound around the detector shaft in a manner that allows the connectors to be fastened without producing a sharp bend in the cable. Inspect the cable for cracks in the insulation, small holes (possibly produced by thorns), and abrasions, and patch them with a small dab of silicone rubber sealant or other appropriate sealant. Try to make this seal smooth and unnoticeable. Allow the sealant to cure for at least 12 hours before using the detector.
Check the control housing, as well as the rest of the detector, for cracks, pits, or other damage. In most cases, strong, inconspicuous repairs can be made with clear epoxy cement; apply a fiberglass patch if necessary. For obvious reasons, don't use the metal-filled epoxy.
Secure the coil cable to the detector shaft in two or three places with Velcro bands. This precaution can prevent the cable from snagging on tree limbs or in the brush, thereby damaging the cable itself, the electrical connector, or the delicate connection to the coil.
Strips of this sort can be purchased from some detector manufacturers and they work very well. But you can make them for less by buying a dispenser roll of utility Velcro strapping (Get-A-Grip, or equivalent) from a hardware or home improvement products store, and cutting them to length. You'll have enough for more than one detector, and plenty of additional strapping left over for other uses in the house, garage, garden, or office.
As a final preventive maintenance step, particularly if you hunt in rough neighborhoods, consider the advantages of dressing the detector down by removing or obscuring flamboyant decals and markings, and making your own appearance match the inconspicuousness of the modified detector. Perhaps it's needless to say this, but it's also not a good idea to brag about the capability of your machine to overly-curious passersby, or to discuss the prices of detectors in general.
A well-maintained detector is a happy one. This happiness is passed on to its owner.