I've been playing around with contact mics for years now and unless I've built them into something solid they have all met a death as the crystal surface on the disk is fragile and the solder joint attached to it usually falls off. Today I set about redressing this and made these tuffened contact mics.
Here's how I did it...STEP 1
I connected up the wires (other end is a 3.5mm stereo jack), soldered them and added some hot glue over the wires and the disk to act as the first bit of cable strain relief.
I insulated the wire connections (yep with gaffa tape...thats how I roll!) and then stuck an "S" of cable to the disk to act as a second defense from cable strain.
Finally (and here's the snazzy bit) I covered the entire surface and up around the cable with polymorph...Polymorph is an amazing plastic that you can buy online (I found the best deals for this are on ebay) that comes in granules. You add the granules to near boiling water and the plastic melts and becomes pliable. You have to work quite quickly but I managed to cover these disks well. You then allow it to harden and it is super tough when it's fully cooled. The only other thing I may do to these contact mics is to run a bit of silicon sealant into the bit where the cble comes out to make them fully watertight...then they can be used for hydrophones for underwater recording as well...
As for today...I just clamped em up to a slinky!