From what I understand, you can put up a simple open fence around your AC unit as long as a) the fence is no higher than the AC unit and b) you get permission in advance. There might be other criteria but that's the minimum I was able to find. I think if it's done correctly, with fencing similar to the fences on the patio villas, it'd look a whole lot better than the AC units themselves. I'm probably going to just add a couple of potted plants or add a short (under 4 feet) row of shrubbery or some of those tall pale decorative grass tufts I see in everyone's garden beds. It won't hide the unit completely but it'll make it look a bit less stark and out of place in the yard.

I'm happy our a/c unit is hidden and protected by huge bushes also providing shade for the unit. I keep them trimmed and clean.