If you are putting something on to do the job and it's only for light towing, I'd put it as high as you can on the transom to keep the rope away from the prop. The traditional ring mounted low on the transom is the strongest place but very hard to see the line from the helm especially in a boat like mine where you are seated well forwards in the boat, you really cannot see what the first six or eight feet of line are doing and whether they are anywhere near the prop.
I've always thought it would be an idea to have a very stretchy bit of elastic from a point on the tow line to the top of the A frame so as soon as the tension went on the tow line it would haul the tow line clear of the water, but would elongate to allow a straight tow line under load, but I do so little towing I've never got round to looking for anything suitable or trying it. I guess it's not for nothing that most ski boats or proper ski points are fairly high up!
The best thing is for the person on the other end of the rope to be aware/responsible to keep it tight enough to keep it away from the prop.
A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
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