Cease cutting or trimming any weeds or grass growth around the pond's banks. A principle component of the bullfrog habitat is dense, concealing growth just on the edge of the pond. This gives them immediate access both to the insects that thrive around the water's edge and to the safe haven of deeper water should they need to escape.
Stop using any pesticides, herbicides, or insecticides around the pond immediately. Also, consider any logical pathways to the pond from local streams or waterways, and eliminate the use of these chemicals in between each location. Frogs have extremely porous skin and are often the first to suffer from chemical exposure. Furthermore, much of their diet consists of the insects that accumulate around ponds, and tamping down these populations with chemical treatments eliminates basic sustenance for the frogs.
Plant water lilies or other aquatic plants around the water's edge. Bullfrogs like a varied landscape in and around the pond, and these plants will provide shelter and safety to resident frogs. Avoid aquatic plants that are not native to your area, or which cannot be controlled by fish populations in the pond. Many aquatic plants spread rapidly, and you may lose control of the pond's balance if you select an improper species.
Leave the pond dirty. Cleaning or skimming the pond may be great for aesthetic purposes, but not for bullfrog habitats. Bullfrogs enjoy a murkier, messier environment. This is often where landowners have to make the decision between an idyllic pond and a bullfrog-friendly pond. Beauty will certainly be in the eye of the beholder here, and it is up to the individual to decide whether or not they want a messy pond that bullfrogs love.