lol damn everyones making this so complicated.

heres some suggestions, things i would do

get your parents a big, defensive dog (german shepherd, rotweiler etc)
buy a gun
get a security system
ask your parents to take some kind of simple self defense class
get your parents a gun, or since chowder said they are against guns, get them some pepper spray or something like that
make sure they have cell phones to call for help if need be

and last but not least, DO get a restraining order. Get one just so that you have a reason to call the police if he shows up at your house. If your uncle comes by your house or if you see him around, he isnt breaking any laws-- unless you have a restraining order