The most reliable approach is to combine a physical barrier with a few smart habits. For squirrels, flimsy plastic netting is usually not enough because they can chew or pull it loose. Use a sturdy frame covered with 1/2-inch hardware cloth, or build a hinged wire lid that fits tightly over the planter box. Secure the edges with clips, zip ties, or weights, and check for gaps near the soil line and corners. If you are growing individual plants, wire cloches or metal cages can protect seedlings until they are established. A layer of chicken wire laid just under the mulch can also discourage digging.
For birds, bird netting is effective when it is taut and supported by a frame so birds do not become tangled. Choose a fine mesh that fits your crop and secure it around the entire box, not just the top. Floating row covers on hoops work well for low crops, but remove them when flowering plants need pollination. Avoid leaving spilled seed, food scraps, or open water nearby, because these attract birds and squirrels. Move bird feeders away from the planter area and keep the soil surface tidy.
You can add deterrents such as reflective tape, old CDs, a motion-activated sprinkler, or a decoy owl, but rotate them so animals do not get used to them. Scent repellents may help briefly, but they need reapplication and should be used carefully around edible plants. Choose sturdy containers, avoid overwatering, and harvest ripe produce promptly. No single method is perfect, but a tight metal barrier for squirrels plus well-supported netting for birds will give your urban planter box the best protection.