Sorry Buzz, I only tape the lead to the shaft,...my skid plate is busted and I know I need a new one, but the standard ACE250 coil would be a hassle to put tape around(being a bit small), and just mentioning,...gaffa tape comes in two types, one that has no lead and one that has lead in it,..I always use the lead based tape as it lasts a lot better for the job, and as it's not moving at all it has no effect on the coil input signal (in my case anyway),.. other opinions may differ to mine and results may differ due to detector differences and operator idiosynchronisities(not sure of this spelling,..and neither is spellcheck(ha)),..hopefully some one who uses tape as a skid plate religiously may be able to offer you a more accurate rundown on the whys and what fors of their experiences with tape and coils.
Hope this helps in some small way,
Cherrs(can tell I tried a new drink(getting better now)).
Silver.