Whether you use 6x6 posts and just sit it on the patio not so much as one screw into the deck . with say 4 layers of 6 x 6 in a 8 x 12 box .
Using a good amount of landscape spikes to insure all the layers are locked fully together. sand the top edges so theres no sharp edges. Add non woven fabric across the entire box over the sides across the bottom and up the other side. put in the edpm liner . Secure it with a 2x8 cap place your pvc pipe across the bottom of the bog probably four 2" pipes across the entire bottom and fill 12 to 16 inches with 3/8 pea stone theres a few more steps to it but not many
Using a good amount of landscape spikes to insure all the layers are locked fully together. sand the top edges so theres no sharp edges. Add non woven fabric across the entire box over the sides across the bottom and up the other side. put in the edpm liner . Secure it with a 2x8 cap place your pvc pipe across the bottom of the bog probably four 2" pipes across the entire bottom and fill 12 to 16 inches with 3/8 pea stone theres a few more steps to it but not many