rebar will not be strong enough, 1/2 inch probably not thick enough especially for an O ring dragging across it 1,000 times a day. you gotta use 2 car axels and 1 inch or 3/4 coated atleast if u gonna use metal on metal. for a permanent set up you want to make sure that it's not going to break with a 50 pound dog running it all day everyday. lot of wear tear and friction plus the elements.