In our area, el Perello, we can go to the adjuntament and ask them to advise the local hunting society to mark our land as off-limits. They have to record this and abide by it. Generally they will unless some non members come and shoot. The hunting society "cazadores" may come and put the signs up. It is quite tightly regulated even though it sometimes doesn't seems like it.
If you don't tell the adjuntament then you can't complain!