Indeed. Your best bet, if possible, is to fire it up every now and then and let it run long enough to warm the engine up and recharge the battery - note that if you don't let it run you'll empty the battery since starting takes a huge chunk of charge from it.
Second best bet: a dedicated maintenance charger which will wait until the battery discharges sufficiently and then top it up.
Third - and cheapest! - is simply to disconnect the battery. Self discharge is tiny compared to the leakage via the permanently powered circuits: the central locking system, the alarm system, and (possibly, depending on head unit) the radio.
But those latter two don't get the fluids moving. Best of all is to take the car out of the garage every now and then and drive the damn thing
That's my approach...