What I've learned is that if you provided hiding places it promoted fear in the pet & caused aggression.

The same theory worked on my fish Jack. He was freaked out by me when I gave him a hiding place. So I removed it & now nothing scares him & hes always out begging for food & following people as they walk by.

My friends on a nother forum has semi agressive snappers, as they ALL have a hiding place. Axle NEVER had a place to hide. I also left the tv on for him & took him outside to get use to bikes, strangers walking by & cars. Axle is 95% fearless & being that he has no reason to snap. As snapping is a reaction to fear