Hi @LorenClayton,
Unfortunately, you wouldn't be able to fill in your fencing in a conventional way unless you were able to weld, which isn't a skill most people possess. This is because fillers need a backing for them to stay in place. The surface area they would be clinging to is just the edges of the metal, which will not hold.
You could, however, use a pair of aviation snips to tidy up the edges, hit them with a file if needed, then give the edges of the hole a quick coat of Etch Primer and Surfmist Touch Up Spray Paint to protect them from rust.
You could then cut a piece of Aluminium Sheet to cover the hole, then drill some holes through the sheet and the fence and install it with some aluminium rivets.
Once the sheet is in place, apply the same primer and spray paint to cover the patch and blend it in with the rest of the fence.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
