Fox Cubs biting off Tulip heads.

We have a fox and five cubs living at the bottom of our garden. We have been rubbing along nicely and they have been quite entertaining as they play on the lawn. However recently they have startied digging in one of my borders and I regularly find the heads bitten off emerging tulips. A friend suggested some hot chilli sauce on the stems. That seems a little cruel. I've tried an ultra sonic device but this was useless. Has anyone had a similar problem? Any solutions?