Another kicker is that those ferrels can be crafty bastards. I saw one on animal K-911 (or whatever the hell on An-Plan) bat the can of tuna with its paw from the outside, knowing it was a trap. so keep it centered towards the back of the trap, and if that fails, maybe hot glue on the bottom.
I had this fucking peeping tomcat. No shit. It would leap 6' (probably with a ledge as assistance) to sit on a window A/C unit and spy on us. The thing was that it would make an unnerving thud at 4am, or if it had camped out my gf would scream as the gleaming eyes met her field of vision from outside.
I bought four 4-packs of those mouse glue traps and set them on top of theAC unit one day. 24 hours later I heard BOOM! BANG-A-LANG! (never heard a bang-a-lang before). I noted with great satisfaction only 12 traps on the AC and 2 on the ground so that fucker was off somewhere dealing with two of them. I reset the two and went inside. Two days later (daytime now) I hear the apocalypse out there. I run out and see 3 missing and one of them has a crow feather stuck to it. The bird was nowhere to be seen and the cat never returned.