Refuse to go up the RAMP!!

For a couple years now we've used a ramp up into the back end of the CRV as Cowboy's arthitus and spine bothered him to jump up into the back.  So we put up a doggie ramp that he would go up. But he always has a tendency to slide a bit on it  due to his nails or fear or somethng...anyhow he flattens out now on it and it's become a problem.  So yesterday I just put a towel onto the back seat and got him into the car and he sat on the towel...lay down after awhile..  The aging process takes itos toll on us all :(