The trouble with chains and d-locks is that these days, hydraulic cutters are not difficult to get hold of and they're virtually silent. There's not much will stop one of those.
The idea is to make sure the scrote(s) will draw a lot of attention to themselves when attempting to relieve you of your property. So to that end:
Halogen PIR. Biggest, brightest one you can find.
Solid timber garage door. Openable only from the inside, for preference.
If you have a side door, also solid timber, with deadlocks and hinge posts. If you can afford it, phone CR Smith and ask for the 'drug dealer special'. Okay, don't ask for that, but there's a model they make that is favoured by the vendors of illicit substances as it'll stop not only their competition, but most police 'enforcers' too.
A *loud* siren alarm. It may be fairly trivial to disable, but if it's difficult to get to, that's not going to matter - if it's effective for 30 seconds, that's likely enough.
*Don't* use toughened glass in any windows, if you have them. That may sound counter-intuitive, but toughened glass shatters into nice safe clumps. Plate glass doesn't - it breaks into vicious shards of all different shapes and sizes, making highly likely that your average scrote will puncture themselves repeatedly trying to get past it. If you have windows, some form of reinforcement behind them is a must.
Of course, with the halogen and the siren, care must be taken to make sure they don't go off when they shouldn't - your neighbours will just ignore it, if that's the case.
Also, secure the surrounding area. If your fence is over 2.4 metres high, you're perfectly entitled to glue broken glass to it without the risk of being sued. If you want to go for subtle, carpet gripper nailed to the top and painted the same colour as the fence is a remarkably effective deterrent (If the fence is lower than that, you can still do these things, but you increase the chance of the scrote suing you for personal injury). Secure side access to the gardens, etc. as well.
Some of those may have been recommended to me by a local PC. Some may not. Some might have been, but it's highly unlikely the PC can officially recommend them