I do a lot of pads for people, so I like to hot glue the wires down just to make sure they don't come loose.  If you are hacking your own pads, I would probably reccomend that you do it, too.  It makes it a lot less liable to pop off.  As for what kind of glue gun, I bought a cheapo $2 gun that uses mini glue sticks.  It does the job just fine, and the refills are cheap, like $3 for 100 sticks.