What about a heating pad that goes under a bed. My cat has one. It only warms up when they lay down on it and it doesn't get to hot. I used it to help germinate seeds once. They just get warm.
For the cat we just put a towel over it, but if the dog chews on stuff it probably would be good....
Riley - 11/05/2012-8/30/2013 (Myasthenia Gravis)
He will always be in my heart.