We have a special rug that can be rolled up easily by any child old enough to be playing with these toys in the first place. Even if they swear to stay on from now on, once they purposefully walk off the rug, blocktime is over. They learn quick.
Consistency is key, here.
Anyway, when it comes time to clean up, it's very easy to put the blocks away because they are all in one relatively small space. Simply store the ones that 'get away' in the vacuum cleaner. I bought the kids two rugs a few years ago at Lowes Home Improvement store. One has city streets on it and the other has a construction site decoration. We have used this idea with leggos and toy cars.