Feral cats know where to go to forage for food or find a safe place to sleep. The less hospitable you make the outside of your home to these cats, the less likely it is they'll spend time in your yard. You don't have to use cruel tactics to dissuade these cats because there are plenty of humane options available.
The less comfortable you make the ground surrounding your home to walk on, the less likely cats will be to walk upon it. Coarsely cut mulch, for example, will not injure the cats' paws, but it might make them turn around and walk away because it's uncomfortable to walk on. Products like Scram for Cats sprinkled on the ground helps repel cats without harming them. Vinegar and mothballs are also said to repel cats because they don't like the smell. You can also make your own cat repellant spray using natural ingredients.
Motion-detecting sprinklers greet feral cats with not only a spray of water, but also a hissing-like noise upon activation that cats will respond to by fleeing. Soaking cats isn't inhumane, but it is effective and can keep them away. Cats are smart and if they realize that every time they walk onto your property they run away soaked, they'll quickly learn to avoid your property altogether. Purchase a motion detecting system specific to animal deterrent for less than $100 from Amazon.
Cats can hear some noises that aren't detectable to humans; broadcasting sounds that make cats uncomfortable will keep cats away without hurting them. Many units are available that will sense the presence of small animals and broadcast the noise to repel cats, dogs, and other small animals. The Solar Power Ultrasonic Cat Dog Repeller is an example of these units and costs around $15 per unit. Place these units in your yard where you've witnessed feral cats, and the unit will sound when motion is detected; humans will not hear the noise at all.
If your neighborhood is overrun by feral cats and there's simply no keeping them away, consider giving them a spot to live away from your home. If you have vast property or if your neighborhood can agree upon a community spot and it's not in conflict with local ordinances, create a place that will attract these cats to keep them away from your residential area. Plant catnip, provide ample shrubs, and make it a spot cats will love so much they forget all about your property.
Avoid leaving food outside of your house, either for other pets or in an open trash can. Realize many feral cats are merely looking for their next meal, and your trash - or the little critters attracted to your trash - may prove irresistible to hungry cats. Talk to the people living in your neighborhood to dissuade them from putting out food for the stray cats and explain their actions are compelling cats to hang out on your property.
Reduce the Feral Cat Population
The Humane Society of the United States endorses trap and release tactics that include spaying or neutering feral cats. With this process, these cats are humanely trapped, taken in to sterilize, and then released. Contact your local Humane Society for help with feral cats on your land. While this won't guarantee the cat won't return to your property, it reduces the potential of future cats claiming your property as their own.