Do a respray and then 3M it. I did that with my E46 and it underwent 25,000kms of multiple US roadtrips. The 3M did it's job and not ONE chip appeared on the bumper.
Going to do the same on the E39 in a month or whenever it's on the road.
'02 ///M5 Imola Red / Imola Red '09 335i Alpine White / Coral Red
'04 E55 AMG Brilliant Silver / Anthracite
'96 318i Alpine White / Black
'01 330Ci Titanium Silver / Coral Red
'96 328i Jet Black / Black