Perfect feature! Love the idea!
Something like this would be fun.. rope net with some sea creatures.
If you're going to put a perspex mirror on a fence to visually expand the size of your garden and make it look like the fence is not there then please put a trellis over it to break up what appears to them to be a way to fly thru'. Birds in my experience don't fly directly thru' trellis but over it, so playing trellis over the top of a mirror should avoid bird injuries. It might not achieve the look you're wanting, but unless you want dead and injured birds in your garden, its the best way to avoid unwanted damage to the wildlife.