Single door is easier. On the side that the door opens toward (the non-hasp side), install a pipe or L bracket to keep the bottom from being pushed in or pulled out.
Then, on the hasp end of the door, you can install a 3/8" rod (or lag bolt if you have a wooden jam) into the door jam near the floor that sticks out into the doorway 2.5" or so, and a bracket on the door with a 3/8+" hole in it that matches up to the rod. The idea is that when the door is closed, the bracket will slip over the rod to keep the bottom from being moved in or out.
This is the same concept on hinged doors where the hinges are installed on the outside and the hing pins can be driven out of the hinge from the outside. (When the hinges are on the outside, someone can drive out the hing pins and open the door from the hinged side instead of the lock side, unless, of course, rods have been installed.)