Hi Tiggy's mum,
My fence went up about 18 months ago and yes I have one little soldier who found all the loopholes but after watching how he escaped solved the probspretty quick. He found his way up into the cherry tree and also found a launching pad from a woody shrub at first, so I wrapped some of the spare perspex like a collar around the tree trunk so he couldn't scramble up to the lowest branches. and I used some plastic roof edging, the stuff that goes under the bottom row of roof tiles which extends into the gutter, It's shape has an incline, I slotted it behind the perspex so it leaned into the garden a bit, which added just enough extra height and incline to stop him attempting to get out. The garden sheds aren't a problem because they can't jump high enough to either scramble up or jump directly on to the roof. Window ledges etc are far enough away for them not to be able to launch themselves over the top of the fence so everything is now fully catproofed.
I had to enlist my brother with his drill (I'm rubbish with a drill) to drill holes in the concrete posts and the iron posts and bolted the wooden batons to those posts, Then drilled (carefully) holes in the perspex. Using rubber washers, to cushion the tightened screws and just screwed the perspex to the wooden batons. Each panel was overlapped a few inches, drilled and fastened together with plastic garden ties.
Dead simple really... even simpler with wooden panel fencing, due to not needing to drill and bolt concrete and iron... lol
P.S. Perspex can be a dog to cut, especially the corrugated stuff (flat perspex is very expensive) I think my brother used a very fine jigsaw blade to cut the piece for behind the gate, a course bladed saw will crack and break it, drilling also needs to be done slowly and carefully so not to shatter it. but it can be simply overlapped to fit so cutting wouldn't necessarily be required, apart from maybe behind the garden gate
Ideally you can't have anything close enough to the fence to allow them to gain any height and subsequently launch themselves over the top. but if you have a tree that you don't want to fell the only solution is to put a collar around the trunk and make sure the lowest branches aren't low enough for them to jump straight onto them from ground level, otherwise some low branch pruning would be required.
I used some spare perspex for a collar for my cherry tree and wrapped it round the trunk, extending 2 feet down the trunk from directly under the lowest branches and fortunately it was enough to stop little Woody (pic attached) escaping.. If any trees you have a smallish trunk, the biggest buster collar that vets use could be used to wrap round the trunk or you could make a collar from wire coat hangers fixing netting or fan shaped segments of perspex to it so it looks like a big plate, with a big hole in the middle so it fits round the trunk. It needs to have a split from the centre to the outer edge like a buster collar, in order to wrap it round the tree. it can also be suspended with string or wire from higher branches so it doesn't flop down. If you can't picture what I'm trying to explain I'll have to try and draw and photo something then post it.
Purrlishious... Thanks for the catnip/catmint suggestion, it's about the only one I actually know of.. and grass of course... lol