Kim - LOLLLLLLLL! I understand big dogs wanting to help with the gardening.. I have 2 medium dogs and one would LOVE to help me garden. I used to have a huge golden retriever who would retrieve anything, including new pine trees that I had just put in the ground!!
I ended up breaking my yard up so that they had their area they could destroy (which they did) and then *my* area where I could plant whatever I wanted. And it worked!