Hey Pugs.
I'm not a fan of grills so I was faced with this dilemma at one time as well. Not sure if this will be helpful to you but it worked in my situation.
I figured any toying my kids were gonna do with my speakers had to do with them being curious and intrigued. I literally spent some good time with them taking them up to the loud speaker and showing it to them, letting them touch it with my guidance and teaching them about it in terms they could understand at their level. I also assured them that it was okay and even good that they were curious about them and if they wanted to touch them they could so long as I was with them. I was pretty emphatic about that last point with them. This worked well for me and after a few times of them wanting to visit the speakers and us going together, their curiosity was pretty much satisfied. As an aside, this also served in teaching my kids respect for other peoples property and obedience.
I should probably mention I have two boys and that the youngest doesn't have any arms and the oldest was 26 years old at the time.

Na! I do have two boys though who, at the time, were two and four.
I hope maybe this gives you some ideas anyway. And, I hope the Loreleis find a home with you.