This isn't very useful but oh well..
The tubs I bought have heavy duty clips on them.

If you look at the sides of the tub, you see 3 black lines and the clip folded under. The clip folds up and snaps shut on the lid. These are used for non-rack systems so that I can use them for quarantine with the lid. The tub is VERY thick plastic and can't be bent in the middle for escape so the clips have to be pulled from above-sideways to be undone in order to get out.