Arrest that slippery seat post! - Simple, cheap mod

My bum acts as a hammer over unduly ground when i cycle.

The seat post gets pounded lower and lower.

My legs now does not extend fully and my knees hurt.

Arrest that slippery seat post!

Its a simple heavy host clamp that costs $2.60
The copper washer is used to protect the plastic seat post shim, preventing the clamp edge to cut.

The final look.