As crazy as it sounds I've been thinking that maybe a predator scent or urine might do the trick... some of these are a bit pricey too but a lot less than having a fence installed.
I've been looking at some of these recently on googles search engine and you can find a cotton type wicking system and scents a plenty. I imagine you might have to freshen the wick after a good rain but a drop or two of this stuff on each wick can last a good week. I've used other scents while whitetail hunting using these wicking systems to attract or masking my human scent. I imagine that the urine scent of a predator might work at keeping them at bay.
