Are your dock posts sitting on lake bottom or screwed in?
I’ll assume screwed in, otherwise don’t think your be asking...
Anyway, my additional comment would be to find way such that the rope is at the bottom of the post where is it anchored to bottom of lake vs tied to dock, which would cause the dock to “teeter” back and forth. If that makes sense.
Make a loop on end of rope or get a metal ring to go around iir that will drop or a u-bolt. Many options.
Is your boat uncovered in the snow? Whole ‘nother conversation there...