Over the last few months, I have researched using a trolling motor to accurately anchor, without all the faffing of chains and ropes.
Best in class appears to be Minn Kota and to be fair, their technical assistance from the states has been outstanding. I will be using a bow mount terranova, however whether it will be 55lb or 80lb is as yet undecided. 55lb is adequate for my RIB, but 80lb would give an added comfort factor.
The spot lock system should hold me within a 1m radius (probably better), for a period of about 7 - 10 hours. An added bonus is the fact that I can use it as a bow mounted aux, and it will give me a little under 5 knts (SOG) for about 5 hours.
I am now working out the installation detail as the Minn Kota will be mounted on a quick release plate.
Not cheap, but a good solution.