Dog proximity sensor

Hey there!

So, I like to dabble in this stuff…but its strictly a distant hobby of mine. I need a good pointing in the right direction. I have a dog…and lots of cats. The dog likes to get in the litter boxes and eat the cat’s poop. Im thinking I might be able to hack a citronella dispensing anti bark collar into a deterrent that lives at the entrance of the cat box. Any time Babe (and only babe) comes near enough, this, dog collar squirts citronella(which dogs hate) into the air. For obvious reasons, I cant use a simple prox sensor that senses movement and dispenses the citronella. So I figure I might be able to make something that attaches to Babes collar, and make something that is stationary on the lid of the litter box that detects the object on babes collar, and out it shall squirt. Any suggestions on what might work? What type of sensors I should direct my attention?

Thanks,

Adam.

RFID tag on the collar and a custom RFID reader coil around the entrance of the litter? Seems like that is the most targeted way to activate a deterrent.

Works for milking cows anyway.

Or if it already has an ID tag implanted try to figure out how to detect that.