Yes—you have plenty of good options. For a dog park, the bench you want is made from a non-porous, rust-proof material and has an open or slatted seat so water and dirt fall straight through. You should be able to spray it with a garden hose, maybe hit it with a mild cleaner, and let it air-dry without worrying about rot, rust, or odors.
Recycled plastic or HDPE lumber is probably the best all-around choice. It is solid, moisture-proof, color-through, and easy to scrub. Brands like Polywood, Trex, and similar recycled plastic bench makers produce heavy-duty park benches that resist urine, mud, slobber, and sun. Because there are no wood fibers to absorb moisture, smells do not soak in. A quick hose-down is usually all it takes.
Powder-coated aluminum is another great option. It is lighter than plastic lumber and resists rust, especially if the frame is heavy-gauge and the hardware is stainless steel. Look for slatted aluminum seats because the gaps allow water to drain quickly. Thermoplastic-coated steel is also tough and easy to wash, but check that the coating is thick and scratch-resistant; once the steel is exposed, rust can start. Stainless steel is the most bulletproof, easy-to-sanitize choice, but it is usually more expensive and gets hot in direct sun, so a shaded or lighter-color option helps.
Molded resin or polypropylene benches can work well on a budget. Choose UV-stabilized, heavy-duty commercial models with drain holes or slats, not the flimsy residential ones that can crack or blow over.
Avoid untreated or heavily oiled wood, even if it looks nice. Wood is porous, holds urine smells, grows mildew, splinters, and needs resealing. Cushions, fabric slings, and padded surfaces are also poor choices for a dog park because they trap moisture and dirt.
The easiest bench to maintain will have smooth, closed surfaces, slatted or perforated seating, stainless or coated hardware, and no deep crevices. If possible, place it on a concrete pad or compacted gravel with a slight slope so the rinse water runs away from the bench feet. For dog pee or stubborn smells, use an enzyme cleaner or mild dish soap with a soft brush, then rinse. Avoid pressure washing too close to coated surfaces—it can chip the finish.
If you want one simple recommendation: get a commercial-grade recycled plastic or HDPE slatted park bench with stainless steel hardware. It will handle the dog park, hose down in seconds, and still look decent for years.