I want to make two 8ft tall pillars 8ft apart at the end of my driveway to mount a sign between. I have done a few small retaining walls but that is all. I want to get more into hardscaping and thought this would be a great project since if I mess it up it is just for me . My question is does unilock make a product that would work for this? Do I need to mortar them or could I use the adhesive you buy from them in the caulking tubes? Thanks in advance for any help!