Not all clowns will feed their anemone. You may want to cover the anemone with an inverted strawberry basket while it eats. I have a perc that steals food, I am usually able to just keep my hand in their near the anemone long enough to keep the clown away. Once the anemone gets a strong enough grip, the clown doesn't take it. However, Maroons are rougher than percs, and this may not be possible in your case.