I wasn't sure which thickness to use on a driveway widening project with a slight slope to it. I decided on the 4 inch thick option as some reviews for the 2 inch thick option stated the thickness was inadequate. I put base material down under the Geo Cell Grid and put weed barrier over the base material. I then installed the Grid and held it in place with rebar 'J' hooks I purchased on Amazon. I filled the first two inches of the Grid with more base material as it is considerably cheaper than the granite chips I finished the project with. I removed all the 'J' hooks after filling the Grid with the granite chips. The final result looks good to me and I have driven my truck and trailer over the Grid and nothing has shifted thus far. Time will tell how it holds up but it seems very sturdy with the total thickness of 4 inches of base material and granite chips. (I tried to add photos but they were larger than what is allowed).