The best guards of all: four German Shepherds. No deer, no raccoons, no coyotes, no mountain lions. Nothing comes onto my farm including the two-legged kind that I don't invite. Shepherds are so smart they remember anyone who is my friend.
I actually have 8' fencing around one pasture area, since I discovered that coyotes can easily jump six foot high fences (there are Youtube videos which show coyotes easily going over 6' fences). I used two 4' high "no climb" fencing nailed to 10 foot long 4x4 posts. I also put some 1' x 1' concrete squares ($1 each from Lowes or Home Depot) around sandy areas that dogs might dig in. I didn't have the time to dig down 2' and put in wire mesh to prevent that. So far, so good, although before I had the fence I did lose two sheep.