On the level where touching the sand will cause those sand monsters to come up be sure to drag along sheets of metal, doors, or even a chunk of wood so you want have to walk on the sand. You will have to jump on the rocks at first but those soon run out.
The trick is to use your gravity gun to place your object in the sand and stand on it. Then, place another object in front of it. Jump on it, remove the first object, and place it in front. Continue to do this until you reach rock again and the creatures will not appear.