We looked into prop guards, but decided against due to the lack of performance and increase to fuel use age, the initial outlay and we replace one engine a year, and so don't particularly like drilling holes in the cavitation plate.
Most of our drivers are actually not too bad, but if you are instructing kids it's easy to get distracted.
If someone is planing towards the beach then no, some beeping won't stop them, but when tootling around the beep will just remind them, that's all we are after. It seems that gone are the days of 'Dipping and oar'.
I was hoping that I had missed seeing a simple echo sounder but seems I may have to splash out on £140 see if it helps for the new engine this year to last.