Interesting is right ... i too have never heard of such a thing. Where did you happen to read this? Are any of the ingredients in the cat collar harmful to reptiles? Does whatever soultion is in the collar leach out ( potentially into the substrate )? Did you try to bake or boil your mulch? How strong is the odor of the flea collar? Does it smell when you pick up a piece of the mulch and sniff it ( i know that sounds wierd, but it may have leeched into the substrate )? I've never honestly heard of such a thing, but i suppose it could work. Dont know that i would do it without some research on my own first tho. If you have links to where ever you read this .. i'd be interested in reading them.