I’m worried about badgers. Sure, lay track on soil or turf, and you’ll soon have problems even without any wildlife becoming involved. A couple of rainy or frosty nights later your trains will be rolling up and down newly emergent humps and hillocks. But badgers could really exacerbate the problem. I read plenty of advice that agreed the trackbed needs to be solid and stable, but also that there are several completely different ways of doing this, each with their pros and cons. I’ve not come across any confirmation of which is the most badger-proof.