Best way to protect a motor???

I've got a Neu 2230 that likes to suck in a lot of dirt through the vent holes. It does not have an internal fan but seems to be a dirt magnet. I'm trying to find a way to keep dirt and sand away from it, but still allow it to breathe to keep cool. So far I've thought of:

1. Aluminum tape over all the holes.
2. Custom outerwears filter. (Don't know if that will work without some sort of active cooling forcing air through the filter.)

What are some other ideas that you have used to protect inside a motor without sacrificing cooling?