Rather than install child safety locks on my parents nice cabinets, we've gone the high-tech route: rubber bands wrapped around the door knobs. This works pretty well for now--Lucy's dexterity has not progressed to the untangling phase.
However, the only problem with said rubber bands is that they're a pain, and easy to take off. Thus, our cabinets are unprotected half the time.
Enter Lucy. This girl now lets us know when the rubber bands are unhooked by pointing and saying, "Uh, oh!" She doesn't touch the door or the rubber band. Then she watches while we re-secure the door, and walks away, satisfied that we're staying on top of her safety.