I am having trouble finding 4x4's for an outdoor project right now. I'd like to mount an outdoor television about 5.5 to 6 feet from the ground. I was planning to use two 4x4x10' pressure treated boards about 3.5 underground in cement. There is no wood available right now. My question is can I use a 4x4x8' board (I have 2 of these already) and attach a 2x4 extension on the bottom end deeper into the cement? Or could I possibly use the the 4x4x8 with 2.25 feet underground? The tv is about 95 pounds, so I worry about the strength of the supports for the tv.