Are you determined to use wood posts for this?
Consider T-posts, which just get staked directly in to the ground. Price is somewhat comparable to a 4x4 post and lasts years/decades compared to wood. Comes in various lengths, 10ft is what you'd use for your 7-8ft fencing. When I need to attach wood to a t-post, I use plumber's tape/strapping to adapt it, or drill a hole through it.
Alternatively there are ways to anchor wood posts to the ground without concrete - such as setting them in gravel/rock or gravel/sand mix. You could also use a metal post support such as the fence post mender stakes, t-post, flat-bar concrete form stakes, U-channel fence/sign posts, etc.
Few years ago I extended my run using T-posts and fencing, it works great and was near free as I had most of the materials on-hand already. I used bamboo for additional structure since I grow it, but if I was buying something I'd consider stainless aircraft cable/wire rope, rebar, or metal conduit pipe.