I use a 12v feeder battery zip tied to the tree, and bought a 10 pack of 12v male plugs off Amazon. I connect the pig tail plugs from Amazon to a longer wire with wire nuts then put spade connectors on the battery side of the wire. I wrap the wire tight around the tree and haven't had any problems with critters. Of course as the tree grows the wire will get tighter.
With a Spypoint Micro, a new feeder battery will last 8 mths, and it can be recharged after that.