A few years back a group of us who have always hunted the Nicolet National Forest came across an influx of hunters and trucks parked in an area that we knew intimately and planned to hunt. we abandoned the area for our morning hunt and drove by there on the way back to the cabin. what we found were 6 hunters that had the back of their pickups full of blaze orange dummies. After talking with them, we found out that they did this to deter other hunters from entering the area. if someone walked in, they would see nothing but orange no matter where they turned.
so i thought it was a great idea, but this led to a group laying claim to public property type of situation.
as for use on private property to thwart off invaders/ trespassers is an excellent idea.