To put in context the vulnerability of the plastic hydro fan that cools the rear end - it is completely exposed from the front between the frame rails if you don't have a MMM hanging underneath, and it is plastic. The first fan blade I lost was from a hold down bracket on the hydraulic line that worked loose and slid back into the fan. A skid plate would not have prevented this failure. I didn't know this was the cause until I had everything apart. Dealer was happy to have warranty cover the parts. Second fan blade I lost was from a small stick (smaller in diameter than my pinky finger) that rotated upwards as I drove over it with the rear tire and perfectly contacted the spinning fan. Besides the installed audible warning device (sounds a lot like sticking a pencil into a running fan), there would be no way to know that this was damaged without getting under the tractor to inspect. Both of these fan contact failures occurred at my home, driving through a lawn that is mowed at least once-twice a week, 3" tall grass. In my opinion, the design and placement of this unprotected plastic fan, is a horrible choice of design on Iseki/MF's part. I am probably one of the few that use this machine though without the MMM, so there is a lot more exposure. Luckily I caught both failures nearly immediately, so I don't feel there was any risk of getting the rear end too hot, and both times the other fan blades remained intact, so it was still providing most of the airflow.
The next time I used my brush hog hanging off the 3pt, I was very hesitant to cut anything that I could not have done with my ZTR, and chose to back through a lot of what I needed to cut. Inspected the fan blades afterwards and hadn't struck anything that damaged the fan, but I did spend a few minutes untangling tall grass that had wrapped itself around it. Some of the skid plate designs I had looked at or considered building myself left the bottom of the cooling fins on the rear end uncovered, which means they would only be getting natural air flow (not fan powered). I didn't like that design. When I contacted Bro-Tek to see if they had the new ones ready yet for the GC1715, they emailed me a few pics and looked to be exactly what I was wanting - does not restrict the airflow, blocks the fan entirely, and also provides more adequate protection to the filter, rear end, lines, etc.
Disclaimer - there is not actually an audible warning device on the fan.