Can neighbor wishes2placed rocks, plants, gardens ONTO my fences that's facing their side but had no claims about the fence line

I am going to try and pace along with your questions because the facts are a little unclear. One of the concerns I have on your question is the issue of how you have allowed the neighbor to use your property in the past. In Ohio, if you meet the necessary elements adverse possession takes affect after 21 years (essentially 2014), but it appears this relationship has been mutual and thus we may have elements missing. The next issue has to do with any subdivision restriction or covenants that are placed against the property. Since you found records on the fence being erected in 1993 somebody had to get a permit at some point to erect the fence in the first place due to zoning requirements. I would recommend you get a plat from the county's engineers office or get a survey done if one has not yet been completed. Take that information along with pictures to a local real estate attorney to have a kindly worded letter drafted to your new neighbors asking (1) that they abide by the recognized property lines, and (2) cease and desist using the property as their own. My experience has been it is best to get a 3rd party involved--most of the time if your don't the problems will only escalate and get worse. You may be entitled to compensation for the use of your property and any damages that have occurred so take pictures of everything. Good Luck.