I have seen those two forms and I can’t decide which use is correct.
Unser neue Wagen ist [vor/gegen] Diebstahl versichert
Which of the prepositions below suits the sentence best?
It depends on what you want to express.
If you have a theft insurance (legal protection) and want to mention that, you can say:
Unser neuer Wagen ist gegen Diebstahl versichert.
However, if you want to talk about security equipment (physical protection, like a special alarm system), you can say:
Unser neuer Wagen ist vor/gegen Diebstahl geschützt.