Are but if someone was to drop a ton of sand in the way by mistake.... you wouldn't be stopping them but they will need a shovel

As much of a pain as it would be, the best solution is a gate.. once they have opened the gate to gain access they are trespassing, and I think you'll find that you can get away with just about anything then.... short of shooting them.... but you could get some sheep and say that they were worried  Yesterday I couldn't spell Engineer... Today I are one!
Inventor of the 'Guide-o-Matic automatic wheel alignment tool'
Former long term L322 owner, Up/Down graded to a Classic Tractor!

I feel your pain, had same issue when I worked in Coventry.
Used to block them in with cars parked an inch away & use 1/4 tonne bales of cardboard, many times they had to leave it overnight.
Had a guy I blocked in sat in car for 3 hours waiting was a bit as he should have been on site elsewhere  2011 (MY12) 4.4 TDV8 Vogue
2016 Golf GTI PP

Gone
Audi A4
VW Passat
VW Corrado G60
VW Golf GTI
BMW E30
Mini
Vauxhall Chvette

I still think the two strong and low box is the easiest option.

Drag it out into the middle of the road or onto double yellow even better and then call the police and say a car is parked dangerously and causing obstruction and you think it's been abandoned as it's been there for a day or two


Now I wouldn't advocate this officially and it is of course all tongue in cheek and I would never have done this kind of thing to nonble jockies in the past...  FFRR MY06 facelift With TDV8 Alloys Zeros/ATR's
Mantec Sump Guard, Rigid Load liner, MY10 BT upgrade.

Tow it into the road and call the old bill. I've done it once and they never parked there again. 2020 Porsche Panamera Turbo Hybrid (V FAST)
2017 Range Rover Autobiography 5.0 V8
2018 JCW Mini Cooper
2018 Skoda VRS