You shouldn't have rip roaring current in your fuge, the flow through the fuge should be gentle enough to move the macroalgae around a bit, but not sweep it away.
You can always cut a piece of plastic garden mesh (you can find it in the garden section of the hardware store -- make sure it's 100% plastic and not metal) and stretch that across the top of your baffle or the top of the fuge to trap any stray algae that tries to escape the fuge.