It doesn't sound silly at all! Keeping birds from using your outdoor furniture as a restroom is a common and frustrating problem. Fortunately, there are several simple and humane ways to deter them.
Start by making the area less attractive. Keep your patio or deck clean of food crumbs, spilled drinks, and fallen berries, as these are a major draw for birds.
Next, consider using physical deterrents. Bird spikes can be discreetly placed on railings and the backs of chairs to prevent birds from landing. You can also cover your furniture with specially designed furniture covers, tarps, or even an old sheet when it's not in use. This creates a physical barrier that is highly effective.
Visual and auditory scares can also work well. Hang old CDs, reflective tape, or scare tape near your furniture. The reflected light and movement will unsettle most birds. You can also find inexpensive ultrasonic repellents or motion-activated sprinklers that startle birds when they approach.
For a more decorative solution, place a few realistic-looking plastic predators, like owls or snakes, around your patio. Remember to move them every few days so the birds don't get used to them. Another option is to use a scent repellent, like a gel or spray with a peppermint or citrus smell, which many birds find unpleasant.
Finally, consider giving the birds a better option. By placing a bird bath or a dedicated bird feeder away from your seating area, you can successfully redirect their activity to a part of your yard where you don't mind them being.
By combining a couple of these methods, you can enjoy your beautiful outdoor space without the unwanted mess.