It doesn't seem like you need the stress of a job like that. If you approach this from the position of taking care of yourself and being safe, the options quickly narrow down to these choices - Buy equipment made for this - Hire someone to do it - Maybe a weed cutter (weed whacker). or two - kill all the grass and weeds, place fabric over it, cover with rock - or let it go. Seems most solutions cost money. That seems to be a limiting factor for most of us. I have to tell you - if you said --- am forty years old (or less) and wanted to do this job on a consistant basis - I would say there is pretty good chance you might get hurt and I would not recommend it.
While I know you are looking for a good solution, I know that any solution that affects your health is not a good solution.
Seems like it brings the outrigger to "make shift guesswork trial and error or purchasing something commercial - which is probably not made (because of liability) or too risky or expensive.
Maybe for the good news. Whatever you do, you live in Puxico Mo. It has been hot with not much rain for a while. Grass has been slow to grow and somewhat dormiate. But weeds near a pond have plenty of water. Might consider letting that problem area go. Best Wishes.