Sealing your Urn is very much a Personal Preference and Decision

If you would like to access or are unsure if you will be redistributing your loved one’s remains in whole or part, you might like to use a tacky substance, like or similar to Clear Museum Gel (registered tm) or Temporary Craft Dots. Both are clear and will offer temporary adhesion to keep the lid from sliding if moved. With little effort, you can remove the lid without breakage. I recommend this option, as it will keep the lid on securely. All of our Urns are provided with 3 dots, which are easily removed if you should choose a more permanent option.

For a semi-perminant seal one choice might be clear silicone. A bead of silicone along the top edge of the urn would prevent the lid from moving and would require solvent to remove the silicone. However, there is no guarantee that you will not break the lid if you do decide to open it. With careful diligence and tools, you can remove the seal made with silicone. We do not guarantee that you will not break the lid.
Ultimately, if you would like to permanently seal the Urn, you will likely choose epoxy or a glue, such as E2000 which can be found in your local hardware store.