I need to install a few 6x6's around a gravel parking area at my moms house. These will only hold back about 2" of gravel. Do you think I need to install a trench to hold the 6x6's in place or can I just lay them on the ground? If I just lay them on the ground should I anchor them and if so how? Also I really don't plan on stacking them. I just want to create a boarder. Also if I wanted to connect these together end by end what is the best way.