I agree with some of the suggestions concerning the hobbling method. There are several lunette locks that will work in keeping it from being hooked up to easily.
The fire department I was with didn't have a buffalo, but the local mine did, we assisted with their calls and utilized that trailer a time or two. They had two steel bars through both wheels, one on each side so it couldn't be dragged very far without binding the tire to the frame. It was locked with a padlock and small chain to one tire so it couldn't be pulled out.
They also had a small box covering the valves that was hinged with hidden hinges and locked in place. One key fit all locks and was carried in all of the responding trucks.
For the pintle, they just wrapped the tow chains through and another lock. Even with all the known issues with vandals, no one touched that trailer.
I don't have pictures of it anymore, but it was a good setup.