I did not even use padlocks on my course. Instead, I used locking rim lug nuts that are used to secure wheels to cars. You need a special key/socket to remove them. They have no hard edges and are made of real durable metal and are hard to clamp on to. They are more pricey than a padlock, but a lot tougher to remove.
You just have to be sure not to lose the socket! You can put petroleum jelly in the lock to keep the dirt out.
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