If you say yes the first time, it becomes the accepted norm, they then get offended when you say no on another occasion. I have found my life is quieter if it is just no from the outset and set out the clear boundaries.
I know just now that someone would like to come over and play football, but if I agree once, it will continue for the next decade, so I have to be resolute.
I did have great success previously by being less than optimally dressed (almost naked) during hot weather on a garden chair. (Neighbours kids had not only been trespassing, but were inviting all their friends round to use the trampoline - when I hadn’t invited anyone into my space)......I was “faux-shocked/surprised” and rather slow to grab a sarong and cover up the next day when they all appeared. And they never came again! I can recommend this tactic.