We have used the word finished and put up our hand with a little boy we had with ASD when he did something inappropriate . We then redirected him to another activity we know he enjoyed. If his new interest is pushing can you find something more appropriate for him to knock over like maybe skittles. Our little boy went through a stage of wanting to pull mobiles down and so we said finished and took him to look for some thing else he could pull. I know every child with ASD is different but I hope these suggestions might help. We are lucky and have a fantastic out reach worker who came in regualrly to give us advise and strategies does your LA have any thing similar? Good Luck you sound like your doing a great job helping him to feel safe and secure.