No I never tried an enema of ozonated water. I would wonder about its benefit in an enema.
Retention enemas should only be a small volume, say 1 or 2 cups (There are exceptions of course). Also you should take a cleansing enema prior to taking a retention enema.
I don’t know what magnesium has to do with retention nor have I heard of any object placed near you would help with retention. An inflatable nozzle, either with a single bulb or a double bulb, would help with retention. Many people use this type of nozzle with a large volume coffee enema, usually 1 quart and over.
These inflatable nozzles are quite expensive and are obtainable from a number of colonic supply stores on line, I am listing only two that I have used. Both are very reliable.