To counter this, I think it wouldn't be a horrible idea if almost every tournament implemented a rule that "each round you must use a different mark" or "different deck" or 'variant of 10 cards' or something like that.
It would be too easy to cheat. Also, I don't think that really solves the problem. It would not be hard to make 4-5 decks of different marks with each deck as strong as any other of them.
Anyways, as of my own idea, I think there should be a vanilla tourney; creatures with an ability are banned. So no graboids, lava golems, phoenixes, etc.
If you want more available cards it could be semi-vanilla; creatures with an active ability are banned. This would allow voodoo dolls, mummys, anything without a skill that can be lobotomized.