Most of the little $hit$ that steal bikes, are only equipped with simple tools, like a battery powered angle grinder, bolt cutters, and the like.
If you know a smith, have him make you a steel lock bar, that you can mount in the floor, make it 30mm diameter, as that's toothick to cut with a battery powered angle grinder. Secure it with a large (M20 and up) simple countersunk hex bolt, that requires a larger hex wrench than any of those monkeys has along.
If you really wanna guild the lilly, wrap the steel rods in Kevlar or similar. That will make a mess of any angle grinder.
Not saying this will be 100% safe, but it will make most scum give up, and go steal somewhere else.
Making the garage a pain to get into, also helps. That's fairly easy to do.
In general, what seems to work, is something the monkeys are not familiar with. So anything the local smith can do, will beat the most expensive lock you can buy.