Sarin Bones. Not cheap, but well built and very adaptable. I have the three bike version, and it held three bikes securely for our staycation.
That's a good point. If the lock was around the frame it would be difficult to make away with.Most of them have several straps that would make it difficult to get away with it easily but no proper theft prevention.
Get a proper lock to tie round the frame too.
I don't think someone is going to be able to quickly run off with a 20kg bike!!!
I had a roof rack so can't really help with tail racks. But I'm sure security won't really be an issue.