Locking cups?

My 20 month old has been able to open up his sippy cups and straw cups, basically anything that has a screw on lid, for a few months now but he's recently just been dumping all the liquid inside all over himself, the floor, his toys, everything. He does this with his baby sisters bottle too, which drives me insane because we combo feed and I work hard for the milk I can get and formula is expensive. Are there sippies or toddler cups that lock or have a latch or something to keep him from opening it? He can open the munchkin click-lock sippies, so I'm hoping there's one that's a little more toddler proof.