The more I cogitate, the more I think cameras are the way to go. Dye-based sprinklers do sound like fun, though. And you want to know what really sounds like fun but you have to figure out how to contain the shrapnel? Motion sensor mature zucchini trebuchets!
LOL. It would be nice to have something that would scare them, maybe even get them wet, but I wouldn’t want to really hurt them really really bad.
I also don’t have the money to spend a lot right now, but home security system is on my list of things for hubby to research.
You could stud the front yard with zucchini-loaded Claymores. Zucchini shrapnel is just messy and sticky, depending upon the maturity of your ammo. It won’t hurt them.