Almax, Squire or Pragmasis huge ****-off chains aren’t thiefproof but as near as damnit- they need a powered attack to break and it’s like sharks, you don’t have to be indestructible, you just have to be not worth the hassle. I really like Almax, they did more than anyone to expose the bike chain confidence racket but you can often find Squire on sale, and the Pragmasis pin lock is cheaper and better than most padlocks.
Onguard Brute is an incredible value huge ****-off D-lock, if you prefer that route. I don’t know how genuinely strong it is but it’s too big to crop
At the end of the day you can’t chain all the bits up though, my locks beat our thief but didn’t stop him nicking spares and ripping bits off the bikes. If he’d had time we’d have come back to a load of frames.
I’ve added a new thing, some cheap alarm padlocks. These are junk, but I clip them to the saddle rail, so you can’t move an individual bike without an alarm. It’s loud enough to be unpleasant and it makes a ride-off obvious as they alarm their way down the street. They cost about £6 each
Motorcycle Sold Secure Gold would be a good start this is a much higher standard than cycle Sold Secure Gold.
It’s still crap, though. With big locks it just doesn’t test the methods used to break them so the majority of sold secure gold locks can be broken in seconds.