Introduce surfaces/conditions where it's not possible to defend like a mad man, run down everything and retrieve every ball, and they won't be able to dominate. Nadal, Djokovic and Murray are only above the field as long as the conditions allow them to play their perfect defense.
They are the best defenders the game has ever seen, hence their edge over the field. In surfaces where that particular skill isn't rewarded, their invincible aura will no longer exist.
If only I had that power...
But clay should never be a fast surface, and Nadal does indeed deserve to dominate there same with grass needing to be fast and Federer should be able to dominate grass like he used to. It's the fact that we have insanely slow HC is what pisses me off (almost as much as those bolded country abbreviations