I don't think you can lock the buttons on the box. Perhaps a deterrent to keep the cat away may help some sort of citrus smell usually works as cats don't like it.
Try orange peel looks a bit unsightly but a cheap way to find out if it works,I'm sure there will be some thing you can buy for this type of problem.
Just found this
http://www.deteracat.co.uk/indoor-ca...t-sprayer.html