Step back about twenty years ago; My then partner (Ben, now deceased) and me, laid out a grid on a local park using spray-on, water-based, grass marker paint. Several things happened as a result. Yes, we did find more stuff with some of it expensive jewelry. Secondly, we got dozens of people coming up to us asking what the hey we were going? The park department noticed and started asking questions as well. The net result was, in my opinion, unwelcomed attention. I suggest folks not to repeat the experiment. This said....
I purchased a decent, pocket-sized GPS unit. I don't remember the model, but it was around $500. Out in the open, it was good enough you could place yourself within a yard or two of where you left off. Using local landmarks (trees, park benches, etc.) a person could cover almost all of any given location. I didn't think of it as gridding off an area, but looking back on it, I suppose it was. Nowadays, a decent smartphone can do just as well, or better, if you use one equipped with satellite phone service. I've not tried, but factory literature suggests pinpointing down to a few feet worst case.
Alas, I have ceased worrying about gridding, as I use detecting more for exercise than I do finding stuff!
