Use the hand shovel to remove the old dividers. If the separators are stuck to the concrete, you may need to use a hatchet or axe to chip off pieces until you can get them out.
Look for roots along the concrete. If you find any, chop them up with the hatchet, as they will prevent you from putting the new separator in properly.
Use the tape measure to find the width and length of the gap between the slabs of concrete. The gap is usually in the 1/4-inch range.
Buy new separators and separator nails. Regular nails will not work.
Put your concrete slab separators in the gaps.
Use a mallet to knock your separators firmly into place.
Hammer the separator nails into the slats. Space them evenly across the width of the area in which you're working.
Check to make sure your separators are not rising above the concrete. If they are, hammer them deeper down with the mallet, then repeat step 7.