Background - we live with 3 strictly indoor cats on a second floor. To provide them with enrichment, we give them some supervised time on our deck (we back to trees and and a retention pond, so there's a lot of bird/squirrel activity). We are, however, concerned about one of them dashing off the deck. Partially because of the 12-15 ft drop and largely because of everything else that can happen when an indoor cat goes running off into a strange outdoor environment.
A solution we've considered is having them in harnesses when on the deck. However, looking at harnesses they all look like they'd be a bad way to hold a cat based on where all the weight would be getting distributed. And even with dynamic leash cord, there's going to be some shock from even a few inches of drop (as someone who's done a bit of outdoor rock climbing, I've some experience in that area).
So my question is: is this just a terrible idea we should abandon? And, if not, is there a type of harness that wouldn't be harmful even when the cat is suspended from it or it is subjected to a sudden shock?