I've read about
airbrake safety catches that won't allow extension past a
certain point (minimal) without deliberately releasing
them.

Its called a Pigott hook. Look over the DG website at
http://www.dg-flugzeugbau.de/ then 'innovations' and 'Pigott-hook'.

Invented by 'The most famous glider pilot in the English speaking world' (
note: 'English speaking world' not American speaking world)

:-)

Ian