I have a man made fibre glass pond that I want to fill in, it is now empty, however do I need to puncture the base and sides of the fibre glass prior to filling, unfortunately I cannot remove it as it is too well bedded in place, so I will just have to fill it in as it is. The back garden is all laid with slabs so I am going to lay slabs over it once it is filled in, so will I still need to puncture it so many times in the sides and base?
Absolutely, if you want to grow things there, including grass. Even better would be to remove it completely, then fill in, because unless you puncture it closely all over, some water collection will still happen. You should puncture the sides as well as the base, but obviously, lots of holes in the base are the most critical.