OK, ok so maybe not too smooth to spend £45K on a motor and then 'modify' it with some junk lying around in the garage... but this works pretty well for us.
We have two fox terriers. There was no problem in the previous hatchback as the floor was lower and they were never tempted 'over the top'. There is a bit more room between the headrests in the Evoque and occasionally the larger dog would decide to stick head and muddy paws between them, he was unlikely to launch into the back seats but it was still annoying.
I looked at dog guards but was not keen - expensive, (more) rattles, removing them etc. There are netting things that looked like a nightmare to fix/unfix and were unlikely to look neat either.
I found a couple of old bits of Floguard in the garage and they are an almost perfect fit. They hold really well under the rear centre headrest but needed a couple of mini cable-ties onto the other two. I have not tried folding the seats yet but they are two separate pieces which clip together in the middle.
http://www.screwfix.com/p/floguard-100mm...f-10/12515
Functionally they work exactly as I hoped and after one initial, unsuccessful, attempt to get around the side, the dogs stay low.
Alternatively just stick a 'lampshade' on em... but this one is just temporary.