how to keep mounting ring clean.

I am working on my first fiberglass project and it is going good so far but I could use some advice that I hope will save me time later. I currently have the back, bottom and 1 side of my enclosure fiberglassed. I have a mounting ring up front and have stretched and resined fleece for the remaining sides. The mounting ring was done in a recessed style and was cut to very tight measurments. The sub fits in with no gaps around it which is what I want. However I am concerned about resin and fiberglass running and causing extra unnecessary sanding later. How do I keep the ring free of rouge fiberglass/resin? Any ideas would be great. I have looked at the "How to build a fiberglass enclosure" and see some amazing work but do not know how he kept the ring so clear of material.

Tape, foil, etc... something to mask it while you get messy.I have not failed. I've just found 10,000 ways that won't work.

When you do not know what you are doing and what you are doing is the best -- that is inspiration.