what's a good way to deter strays cats
from coming on your property

there're about 6/7 strays that cut across the
back of my yard all day long it's back and
forth

i can't fence the backyard in because the
senior community i live in doesn't permit
fences and the towns' animal control people
won't round up the strays not unless they
are injured

i have cat droppings all over the back i've
even found droppings on one roof corner
and in the rain gutter

any suggestions would be most welcomed

thanks