How to run single ethernet (no PoE) in trench through garden?

I've never buried a cable before, or even run a conduit in a wall/floorspace, so this is all new to me.

I've dug half the trench across the garden so far. It's only 6" deep in some places as below that I found bedrock. 6" should be fine for this application, I think? But… a few metres of the trench goes under a gravel driveway though, and that's one of the spots where I've found bedrock. Still fine?

I've bought a cat7 SSTP direct bury cable (overkill, I know), but would like to further protect it with a pipe/conduit of some sort. Both from rodents and gravel but also from the compressive force of cars driving over it. Maybe I should lay the conduit in some sand before topping with gravel?

What should I be using, and how careful do I need to be about bends etc if I want to be able to re-run a new cable in the future?

My current plan is just to go to B&Q and see what general-purpose PVC piping they have, but I imagine there's better kit for the job…

Thank you!

edit: the underground run is only about 20m (no, I don't want to use wifi, I'd prefer a cable), and there is a mobile phone mast 200m away about 50m higher up the hillside. I think this probably means that I don't need to worry about lightning strikes too much. Would you still add protection at either end of the cable (it's just running from the main house router to an access point in the outhouse).