Have a look at this quick fastening system from Gun sails for your harness hook. It is also a quick release that you can undo if you get caught up in your harness lines.
Gun have patented the mechanism, but it is retro fittable to a lot of other harness brands.
“The innovative harness safety locking system from Gun Sails is manufactured to exacting standards in Marine quality High Grade 420 Stainless Steel. The claw itself has been made to withstand enormous stresses and has been exhaustively tested in the most demanding conditions.”
More information HERE
At £9.50 it is a bit of a steel! (geddit!)