Tying stuff on roof safely

[Keitai]

Put two rachets on this lot but a four inch fence post is something I wouldn't want coming forward. Any advice ?

 

[Tigercubrider]

seeing as it's a fence post screwing something to the end isn't really an issue.
Then you can use that to secure against forward motion under braking.

 

[cdbe]

Wrap the straps once round the post and tighten. Friction will stop it moving.

 

[foxhole]

I would have the post on top of the ladder so pressure is exerted over the entire load.