You could, but it would have to be fairly long in order to get the incline shallow enough for a dog with limited mobility, and it would get pretty heavy at that length.

Then again . . . they swim to the second step from the top and put their front feet on it. The rear of the dog is buoyed by the water still. They put their rear legs on the 3rd step and push off easily. The problem comes when they reach the top step. Dogs with hip problems have to hop, they can't do that fluid, 4-paw motion required to do stairs, and they don't have the strength to heave their rears from the top step to the deck. Large breed dogs are VERY heavy when wet!

Now I'm wondering if a short ramp, covering just the top two steps, might actually work. Hmmmm . . . another shopping trip to HD