Actually, you can. Aside from the SPr title being available outside of the US, within the United States the AWMA (American Working Malinois Association) decided to implement the new rules / titles as described by the FCI rules, including a stand-alone protection title. Additionally, in the DVG the only requirement to trial in protection is that one of the other two phases also be completed, it can be obedience OR tracking.
Have you ever seen that title offered in a trial? I have yet to see it in any of the trial listings thus far. Not sure why someone would even bother with that. Having completed the ob or tr first makes a bit more sense though.