You might want to consider a prebuilt dock. They are very popular in
my area. They have wheels that allow you to roll them in and out
every year and then the wheels lift up so the dock sits on the pole
structure. The reason people do this is that the ice on our lakes
pushes against the docks every year and eventually moves the supports
enough that you either have to try to straighten them out or rebuild
them. Rolling the dock in and out avoids all the ice problems.