Unfortunately, tigwig, it's in the nature of the beast! I love all my cats, but one of them (little Cleo, bless her!) has just discovered how to catch birds. I feed the wild birds and it really upsets me to see her stalking them (I go & get her & bring her in, if I can), but so far, she's managed to get 2 chaffinches (and possibly a little brambling as well - he visited for a few days & then suddenly disappeared). The older cats don't bother - one of them has always been a mouse-hunter and the other one's just given up hunting anything. Monty is taking lessons in mousing, from his auntie Cassie and Gavin's too fat to chase anything at all!!
I don't know about these collars, I hadn't heard of them till you mentioned them, but I won't put collars on my lot, as we live in the country and they're forever climbing trees and I worry that they'll get trapped. Cassie once got her leg trapped in a so-called "safety collar" and I don't want anything like that to happen again. K xx