Client has a pre-existing 3'x5'x 12" flat thin stone wall to her residential neighborhood. I want to mount my 2'x4'x1.5" redwood/signfoam on top. I feel that small angle iron on sides just wont give it support. Normally would build monument around enbedded post and attached to them.Any ideas? I may have a welder construct a frame and lag bolt to top.