From memory years ago you could get door blank, little metal plates that you put in front of the key lock and this blanked them off.

Apparently was really good because you couldn't just hammer a screwdriver in and turn it

Anyone know if there still available or is it just as easy to pull the rod off the back of the barrel ?

 

Most door locks will just freewheel when excessive pressure is applied, its hammering a screwdriver down the side of the lock barrel that most thieves do. This lets the flick the catch