Our yard has a fenced off dog run in which weeds flourish (we don't have a dog but I assume the former owner's dogs left it well fertilized!). These weeds are large, tough, and fast growing (e.g. thistles, sumac). Usually we apply a strong weed killer each year but now we have a child who will be playing nearby (not in the dog run but in the adjacent yard). Is it safe to apply herbicides in the area or is there another method to prevent weeds? We are hoping to avoid hand pulling because that would be a huge chore since the weeds would keep coming back. Thanks!