If your pushing gravel and you hit an immovable object, out at the edge of the bucket, there is a good chance your going to put a twist in the loader frame. Simple twisting motion is what causes that. The lower the hp of the tractor, the less it would matter, but unfortunately the manufacturers know this, and build the frames lighter on the smaller tractors. More weight and faster speeds also cause twisted loader frames.
I think the best way is to do the pull cart/frame, or as another poster mentioned, put a restraining chain on it to keep it from pulling beyond the 3pt arms capabilities. 3pt arms are great for what they are made for, and will suffer some abuse without fail, but they aren't cheap if you make a mistake and they aren't built to handle side to side motions, only pulling loads.
David from jax
All this from a guy who doesn't own a loader, lol!!
David