Door safety locks - dog/childproof

Some years ago when I took this rescued dog on her first caravan trip she terrified the life out of me by opening the caravan door when I had just popped to the car for something I suddenly saw her galloping off towards the A66!  I had no idea that caravan (and Motor Home?) doors could be opened from the inside when locked.  I raised the point at the time as children could be vulnerable as well as clever dogs.  I rectified the problem by putting a Fiamma grab rail on the outside which I draw across on the fairly rare occasions I leave the dogs alone.  Now the dog is happy in the caravan she hasn't tried to escape for a while but if someone knocked at the door and I wasn't there she would easily jump on the handle (she does it at home and lets herself in which can be useful). 

So at the time someone told me about - I think some grandparents whose charge had let himself out and gone walkabout and they had designed a cover for the lock to prevent this happening.  Does anyone know/remember what it was called?  My new caravan can't take the Fiamma handle so I need something.  It's annoying as I find the handle useful for me negotiating the step especially when parked on a slope as I was recently - big step down!  Interestingly the caravan salesman didn't realise this could happen until he failed to lock me in the caravan to demonstrate!