K.M.
We have those same arms and luckily they do work for us, however we have some glass items out on shelves within our daughters reach. But .... she knows her toys are her toys, Daddy's pots and pans and glassware are NOT hers. Honestly, we just told her "no" from the start and she doesn't bother with our kitchen items. Does he have a set of shelves or boxes that are his somewhere else in the house? Maybe redirect him. Unfortunately, you have a bright one, so I am not sure childproofing stuff will deter him, especially if he thinks there are cool things behind those locked cabinets.
Good Luck.
One thing you can try but they are pricey - the magnets - it is a magnetic hook on the inside of the cabinet - then you have to slide a seperate magnet over the outside of the cabinet to release the lock. My neighbor has these and keeps the outside magnet stored up high, so kids can't reach it.