Post a picture of the gate's situation. Would it be safe if the pivot post is set deep in concrete (with 1-2 rods deep through the post in the concrete) and the hinges are welded to the post and gate? Or! Use good grades of bolt/nuts and bend extra threads to secure bolts.

Been a long time since we had that problem, but as I recall we just used a loop of heavy chain and a heavy duty lock at the hasp and hinge end. Make the loop short and attach it low so that the gate and posts would have to be removed together. This assumes you have large wooden posts at each end. Worked for us, chains are still there, but locks do have to be periodically replaced even with oiling.

Good luck,

Ev