DIY seat lock

Start with an old chain and tube

measure how many links you will need

Use your chain tool to adjust your chain to the right length.

Cut your tube to match the chain length.
Then insert the chain and sew shut.
(I chose to sew tightly incase i cut the excess off later)

close up of chain in tube.

Tube cut and sewn to cover exposed part of chain.
Sew the velcro accordingly.

Final product mounted on bike.
For best results, slide the cover piece up under the saddle rails.