I'm not saying this is the best solution, but it's the one I came up with…
The horizontal bar about halfway up will release the doors regardless of which way it moves. It's high enough so that a very small, eager piglet won't run in and trip the doors. Likewise for raccoons. It's high enough that something that size generally won't trigger the doors. I'd rather have the raccoons eat all the corn and leave than render the trap completely useless for the night. Hopefully, if they do come in, they'll leave something that might yet attract a hog.
There are a couple of things to know. I put a loop of wire around the vertical rod which loosely attaches it to the side of the cage. The first time I caught a couple of hogs, they managed to work the rod loose, and it the process of rooting around the cage looking for a way out, they caught it in a door and managed to accidentally pry the door open. The rod is now secured to the cage to prevent that.
The actually door release mechanism is somewhat complicated. There's a semi-flexible cable running from the top piece on the trigger rod that releases the doors, but I don't have a picture and it would be tough to describe verbally. If you're interested, I can take a photo next time I'm out, but it will likely be a few weeks before that happens due to other priorities.