Some of the quick drains we use have a latch handle with a notch in it that requires you to lift the latch to move it. Probably couldn't move accidentally. Some we use are the ones made by Fram Filters. They are opened by a piece of wire that pushes up the valve that's built into the quick drain. You turn that piece of wire in with the drain hose. That entire assy. is covered by a brass dust cap when you're all done. Those drain slower than the ball valve type, but they are still very handy. They would be impossible to open accidentally.

If your quick drain has NO hole in handle, then drill one & smooth the drilled edges. Get some fine stainless steel wire (you may have to go to local airport & buy some from mechanic) & twist-tie the valve closed to an attached near-by anchor point, preferably forming a 90 degree angle.

I guess it's something to worry about though. If one is really concerned, then leave the factory plug in there & just worry about it not being tightened enough by....? Otherwise, I've never-ever seen a quick drain open by itself or be broken off-though I'm sure it's happened somewhere. I look under a tractor/truck & see 900 other lines-filters-hoses-etc & realize any one of them could be cut or torn allowing juice to run everywhere.