Bench top alignment

When glued together in precarious condition, bench top slabs are going to slide and move, which may result on an absolutely non-flat bench top. The soltion to avoid that is to guide the 2x4. To this end:

1. create a guide with regularly spaced holes (4 holes total).
2. drill holes in each bench top piece of wood.
3. now when gluing, put either trunnion / screw / metal rod in each 4 holes to prevent the sliding.