If you want to keep a park bench from sliding or tipping but you cannot drill into the deck boards, you still have several solid no-damage options. The right method depends on whether you can access the underside of the deck, how heavy the bench is, and how exposed the area is to wind.
One of the cleanest solutions is a deck clamp anchor. These are metal brackets designed to grip the edge of a deck board or wrap around a joist without penetrating the wood. You bolt the bracket to the bench legs or to a concealed base frame, then tighten the clamp until the bench feels stable. If your deck has visible gaps between boards, you can also run a galvanized steel strap through the gap and secure it underneath to a joist or beam. That gives you a strong hidden connection with no holes in the deck surface.
If you cannot access the underside, a weighted base works well. Place two low-profile paver stones, a weather-resistant base panel, or a purpose-made bench weight plate under the bench. Attach the bench legs to that base with brackets or heavy-duty straps. The weight holds everything in place, and rubber pads underneath protect the deck from scratches. This is a good option for freestanding benches in moderately windy locations.
Another semi-permanent option is a high-strength outdoor adhesive system. Use a polyurethane construction adhesive or outdoor-rated epoxy to bond a metal anchor plate directly to the deck surface. Once the adhesive has fully cured, bolt the bench to the plate. The deck must be clean, dry, and sound before you start. Keep in mind this method can leave residue or damage the finish if you ever remove it, so treat it as semi-permanent. Do not rely on double-sided tape or small adhesive pads alone for a park bench.
For decks with gaps or perimeter access, hidden straps and turnbuckles are surprisingly effective. Loop a stainless steel cable or heavy-duty polyester strap around the bench legs and a joist below, then tighten it with a turnbuckle. The hardware stays out of sight, and you avoid drilling into the deck boards. Add rubber sleeves or pads where the strap touches the wood so it does not dig in over time.
If your main concern is sliding rather than overturning, start with dense anti-slip rubber pads under the bench legs and add concealed weight to the bench frame. This will reduce movement on a flat deck in mild conditions, but it will not fully secure the bench in a storm or against strong force.
Whichever method you choose, check the setup after a few weeks. Decks expand and contract with temperature and humidity, so clamps and straps can loosen, and adhesive can fail if the surface was not prepped well. Avoid anything that pinches the deck boards so tightly that it traps water or restricts normal movement. If the deck is elevated or the bench will be used by children or older adults, choose a mechanically clamped or weighted base rather than an adhesive-only solution.