Repairing aquarium ornament

[earhtmother]

Picked this up *new to me* the other day and discovered this hole. Any ideas on how to repair or at least make the edges less sharp?

 

[SaraB]

What kind of materia is it? Can you sand the edges down to make them less sharp?

 

[King Fisher]

Sand it, file it or line it with clear aquarium safe silicone.

 

[earhtmother]

Sorry should have mentioned it's just a large plastic imitation rock, heavy because of its size 17L x 10H x 10W but the plastic itself is paper thin. Silicone on the edges seems the only viable solution