The exact material used to repair a cracked fountain depends on what it is made of -- epoxy-based patching materials usually work best for concrete fountains, while metal or fiberglass fountains can be repaired with waterproof silicone or similar fillers. Turn off the fountain's pump and drain all the water from the fountain. Leave the fountain to sit empty for about a week until both the fountain and the inside of the crack are dry. Clean the cracks with a stiff-bristled brush to remove dirt and debris that may be trapped inside. Dirt left in the cracks could prevent the sealant you use from bonding with the fountain.Prepare the sealant material. If you're using an epoxy-based patching compound, mix the sealant components so they can begin to cure. If you've chosen a silicone-based sealant, mount the sealant tube in a caulking gun.Apply the sealant, making sure it fills the cracks completely. Use a putty knife or similar tool, if necessary, to help the sealant penetrate the cracks and ensure that each crack is covered. For more details http://www.pondpro2000.com/epdm-pond-liner.html