Another idea: Put your feeder on a cinder block, then put bricks around it. This way, they can hop up on the brick, and then onto the side of the cinder block if they cannot reach from the ground.
(OH, on the dog thing - I have 3 very healthy and extremely active, XL size breeds - we feed them each a limited amount, twice daily. They are in awesome shape; I have 2 Great Danes that are the picture of health, both of which will be 9 in July....the life span of a Dane is 7-8 years, so I guess I'm doing something right!)