Discretion is the key. Not just from land owners/walkers/fun spoilers. Bikers can be a pest too. It’s unlikely you’ll be building a fully armoured trail designed for heavy traffic so the less people know about it/ride it the better.
Build whatever features you want to ride, but make them as natural looking as possible (no woodwork). Don’t leave burrow pits everywhere and make any doubles/gaps look ‘safe’. Don’t leave rubbish lying about either – landowners really don’t like that.
I’ve never asked permission and I’ve built all sorts of trails over the years. Most are still about. The jumps tend to be the main target and funnily enough it’s other riders that seem to be the ones wrecking them (i think the size intimidates them 😀 ).
Best tip i can give it sort the drainage out. You don’t want to learn this lesson the hard way.