From this site
Vince in Ireland asks why bother using a search coil cover.
I always use a search coil cover, and I go through several every year.
There are good reasons to use a cover on your search coil at the beach, including protecting your search coil from jagged coral, rocks or wear from abrasive sand.
Anyone who has a detecting lesson off me knows I am a ” Scrubber ” when I am beach hunting.
I like to keep my search coil on the sand when I am metal detecting.
This is the reason why I wear through a minimum of four search coil covers a year.
Metal detector search coils are expensive and sometimes not as strong as you think they are.
Search coils can split or crack, if they are bumped against rocks or chunks of coral without a search coil cover.
The cost of a plastic coil cover has increased sharply, but buying a coil cover is still cheaper than having to buy a new search coil and paying for it to be installed if you own a metal detector with a hard wired search coil.
Spraying truck bed liner or other gunk on your search coil is no substitute for a search coil cover.
Coil cover alternatives, often costs you more in materials and time, spent constantly having to re-coat the search coil.
Sealing your coil cover to your search coil is another bad idea.
Bodged coil cover jobs trying to save a few dollars look bad if you want to sell your metal detector, and may void your warrantee if you send your metal detector in to get it repaired. It’s hard to say you have a bad search coil when it arrives at the repair center looking like swamp thing.
Avoid securing your search coil cover to your search coil too tight, it may cause your search coil cover sides to crack.
I use tape to secure my coil cover to my search coil, but I avoid wrapping it too tightly.
Plastic zip ties are an alternative, but you have to avoid pulling them too tight before snipping the ends off.
A metal detector is your investment in the hobby, protect the end of your investment that takes the most abuse in the beach by using a search coil cover.