What would be the best way to secure posts on a two post free standing shade structure?
We want to be able to remove and replace posts in case of rot etc.
The structure will be 10ft tall, 8ft long, 2ft wide with a roof covered by cloth material.
It will be in a high wind area at times.

I would dig a hole about 8-10 inches in diameter 3 fet deep. Drop in a 4x4 made from AC2 pressure treated lumber. Back fill with fine pea gravel. The lumber should last about 10-15 years and the gravel can alsways be removed later.

My suggestion would be to dig footings for each post (at least 12" SQUARE X 2' deep) and use "column base" hardware (Simpson CB44 or CB66 or equiv.) leaving at least a 1" air gap under the metal base to prevent water damage that occurs by wood's natural "wicking" tendency. Use 1/2" plated or galvanized through bolts to secure the wooden post to the base.