Have you politely let them know they are trespassing?
Another question would potentially be is there additional “community property” after your 10 feet of property area, and they are mistaking the entire area as available to everyone for their enjoyment? Ten feet is not a lot of space, so I can understand why they would practically be sitting on your doorstep.
Otherwise, you might bring the issue up to your board and maybe they could let everyone know in a newsletter to please be aware of everyone’s property space and avoid trespassing.
If you get really desperate … how well to cactus grow in Minnesota?