How big is a rock? Read instructions on line about tune up read reviews. A used quality saw is a good deal, but check blade run out, arbor tilt and easy of use.Everyone has a preference on saws, A saw that has 52 inch table is very nice if your cross cutting a sheet of plywood. A good set of good quality blades is very important ( although expensive), and a good fence. I have an original Rockwell Uni Saw with the tables original fence I tweaked using brass screws to take play out when setting fence. and have no complaints (other than thing is very heavy. Like others I removed the right end table and installed a router table. The fence is about .004 error from end to end, saw blade is about .002 inch from being parallel to miter slot. . Before you buy ensure that the miter slot is 3/4 inch and not an off size. Take your time and a lot of time to tune it up. All cuts will reference off errors. Blades a personal choice I use Freud industrial blades. My crosscut blade was about $100.00 I am getting to old to pick up sheets of 3/4 plywood so I use a quality saw guide to cut plywood down to manageable size.
Do you ever have to many power tools never. My wife ask me why I had so many clamps and I did not need that many, so I ask her why she has many cooking tools. Good Luck and the safety test is which is harder a piece of wood or your finger?