The table saw fence is one of the first things on a saw to wear out with normal use. It becomes loose, and no matter how many times it's tightened, gets worse until it finally breaks and winds up in the garbage. When that happens, build a new one out of wood.
Find the Right Board
Measure your old fence. If you don't have it anymore, figure on obtaining a piece of hardwood 48 by three inches by 1 and a quarter inch think. Call around to the nearest cabinet shop or lumberyard and ask whether you can search through their oak six-quarter lumber yourself. You might have to buy an eight-foot length, but it will be worth it. When you do get permission to look through the lumber, study the grain pattern. Look for the straightest patterns you can find. Some call it "quarter-sawn," or "riff," grain. Every unit of lumber has a few of these boards -- find one.
Straight With No Defects
After you have selected a board, sight down it to make sure the grain is straight. If there's a curve on the end but its straight in the middle, don't worry about it; you can cut the end off. Using a tape measure, find the straightest place on the board and mark it off after first examining it for knots, cracks or splits. If you find any of these, get another board.
Mill It Down
If you are at a cabinet shop, have them cut, plane and sand the board. If you bought the board at a lumberyard, go to a cabinet shop and pay them to do it for you. If you have the tools at home, then do it there. The point is to have the straightest, smoothest board that you can get, and by selecting a board with a straight grain, it will stay that way for years to come.
Clamp It Down
Clean off the top of your table saw. Lightly sand it and the board with 180-grit sandpaper. Take paraffin wax and rub the table saw and the board, working it in. Place the board on its edge, on top of the table saw to the right of your blade where the old fence was. Measure from the blade to the board at the dimension that you wish to cut. Now, for reference -- to get it square -- measure from the top of the miter gauge dado that runs across the top of the table saw to the board. Place a Jorgenson model hand clamp from the overhang of the table saw top to the top of the new board. Now measure from the miter gauge dado the same way at the back of the saw where your stomach touches the saw. Put a hand clamp on the back as you did on the front. Check that your measurement is correct, and still-set it where you want it. If not, take a small hammer and tap it either way, then re-tighten.