Is it easy to grow sea buckthorn in pots anchored into the ground (since I don't have the rights to plant into the soil).
You would need really, really large pots.
Sea buckthorn's roots go between 1.5 and 3 m (5-10 feet) down and on average 5 m, but up to 12 m (13 yards) horizontally, if space permits.
Of course you can block at least some of the horizontal runner roots, but a 5 m tall bush needs a certain amount of root mass not only to anchor it, but also to ensure a sufficient supply of water and nutritients.
Heavy pruning to keep it small is not an option if you want berries.
So all in all, I don't think it's a feasible plan.