Saxifrage are usually small, low growing, flowering plants but if you find a spot that they really like they can grow to be quite large.
Rather than trimming them back, it is easy to split them into multiple plants.
Simply cut through the plant with a spade and dig under the plant 2 inches deep. Saxifrage have very shallow roots. Repeat to split the plant in multiple places.
Round the plant into a nice shape and water well into a new position.