Yes! By the non-mining full nodes validating everything in the network.
thirdprize, full nodes order blocks from the miners, if they're invalid, they will be rejected. All the miner's work will then be wasted.
If a mining pool controlled 51% of the network, they will be able to put through a fake transaction from one address to another. This will pass validation as there is no double spend, no block errors and the nonce is valid. Eventually, by controlling 51% of the network, they will be able to produce the longest chain, thus making it technically valid.
Of course, the community can choose to thwart this by opting for a fork before the affected block, but this is another topic entirely.