You could use something like this and use blu tak to adhere the cover to the front of the speaker...
https://www.parts-express.com/Steel-Mesh-2-Piece-Grill-for-6-Speaker-Black-260-418?gclid=EAIaIQobChM...
https://www.parts-express.com/Steel-Mesh-2-Piece-Grill-for-6-Speaker-Black-260-418?gclid=EAIaIQobChM...