These are the Locking Snaps:
This first one is HUGE. Pretty sure it could hold an elephant!!!
This is the Locking Alligator Snap:
I personally like the size of this one. I saw one in the leather shop that was 1" and a larger body. This one can hold a max strap of 3/4". I'm thinking I'm going to make my next leash out of this clasp.
They're both a +$15 upgrade.
Here they are on a dollar bill to also help with size. The smaller silver one is a nickle plated solid brass locking snap. That one is a free upgrade. However, it must be screwed to open/close every time you use it... so it is a little time consuming. It can not be used without screwing/unscrewing.
I'm also looking at adding either black diamond or petzl locking carabiners as a clasp. Not sure on the price for these yet (probably somewhere around +$15-20 upgrade), I have to decide on which one I want to offer. They will be weight rated though. Is there any interest?