Certified GKH Gardening Expert
Palms, like almost all trees, should always be kept buried up to the same level they've been growing at in the soil. Mounding up sand or other materials around the base of a palm higher than the root-shoot interface will likely kill it.
The exception is if the palm was originally planted too shallowly or if the soil has eroded away, so that the place where the roots meet the trunk is now above the soil surface. This article will help you decide whether your palm can benefit from more soil or sand around its base:
Otherwise, staking should help. If necessary and if the tree is small enough to handle, you can replant it in a more stable way.