<font color="blue"> You need to have good fencing down to the ground and then have the fencing turn horizontal for a few feet and lay on the surface. As industrious and bright as they may seem, I've never heard of one smart enough to back off 4 feet from the vertical portion of the fence and dig under the horizontal portion. </font color>

That's what I did, except that I only went about 18". We'll see if it's enough...