How do you deter dogs from eating hazardous pecan nuts fallen from the tree?

I have 4 dogs & have a fruiting pecan nut tree in their backyard enclosure. Although well fed the youngest dog has discovered parts of the nut are edible & now another of my dogs is showing interest in these potentially dangerous thin shelled nuts. The pecan is like walnuts, with the nut found in hard fibrous chambers inside. The sharply edged shell fragments are indigestible & the sharp shell of the nut can cause intestinal damage to dogs. How can I stop them getting a taste 4 these nuts? Any tips (other than get rid of the tree)? It produces too many nuts over several months to keep raked up. They come down with the wind at random..