Can just one or two cats guard an area against non-sterilised cats?

There must be an optimal number of cats in each area to guard against unwanted intruders. If the area is big and the number of cats few, the small number of sterilised cats may not be able to keep out non-sterilised intruders effectively. It is however, difficult to conclude what the optimal figure should be, as many other factors, such as the area’s density and number of food sources, affect the outcome. Therefore it is best to return all sterilised cats back into the neighbourhood and let natural attrition decide on how many sterilised cats each area needs to keep out intruders.