What type of clowns?
Some clowns just never take to an anemone. Sometimes this is due to them being tank raised vs. wild caught. That being said, I have tank raised Ocellaris that do live in an anemone.
There are a few things you can try:
1) Turn all the lights off in the tank and shine a flashlight at the anemone. The theory is that the clowns with follow the light and once they find the anemone, they won't leave.
2) Feed only near the anemone (works better if you turn off filtration)
3) Chase clowns towards anemone with fishing net (Do not stress them too much. Do not hold them IN the anemone, just push them towards it)
4) Take a picture of a fish hosting an anemone onto the tank
5) Take a picture of a large predator fish onto the tank.
The only method that has ever worked for me is #3