You know every animal is hard to catch. -------That is if you dont know its habbits, and your not on LOACATION.
With cats,
First you nead a FAST snare.They can and will back out of a snare.
Second you nead small cable .Not that 3/32" tow line,that most so called snareman use. Man get away from that 7x7 cable .Sure its good on coon .But thats the only thing I use it on anymore. Go to a Loaded 1/16" or 3/64" 1x19 cable.
Lock ? use a small one. There is a lot of good ones on the market today. Stay away from washer locks .They are now as far out dated as the Model A FORD. Some of them are even so big ,that if they were a ounce heaver they would be Outllawed Cause they'd concidered a Dead Fall.
Loop size, 8"and 8'" off the walk'n surface is a good place to start. .Always adjust your loop to fit your trail.