I was so happy when I received the three trays with wheels.  Right away I went out and put pots on each one.  Much to my dismay, there are no locks on the wheels.  My garden area is on a slant and I have to have something to keep the trays from rolling down the slant, which is normally the locks that all my other trays have.  I am at this time trying to find something to stop the trays from rolling around from the weight of the potted planter.  I really like the trays as it is the first time I have been able to find 16" trays which is great for my pots.  I will continue to experiment until I come up with something that works.  The trays are excellent with the exception of the lack of locks on the wheels.