The reason you use the d-lock on the rear rather than the front (easier to remove admitedly) is cost. The front wheel replacement is cheaper than the rear, remember the cassette comes on the rear.
Best option that I have read is two different types of lock. Thief may have tools for one but not the other. Add a cable in for good measure between the two and should be set imho.
The nice bright orange of a kryptonite will probably stop most and make them look for something easier to have.
Also, lock it up in plain view not hidden away, and try and do it where there are plenty of bikes as the thief will have plenty to choose from.