Our dog did the same, we had 3 tiny holes which ran and turned into 2 longer tears by time we patched it.
We used clear gorilla tape on both sides, it's not pretty but it does the job. When cutting it try to have the ends oval shaped as the corners will lift easier if you just cut it straight. We've used it for about 3 weeks in total since it's been patched and it's still on with no signs of lifting.
If it was someone else's dog I'd be asking for a proper repair or replacement tho.
Hello there and many thanks for the advice. I will bear the clear gorilla tape in mind but for the time being I will keep exploring my options - few as they are.
There are companies that will take out the fly sheet and replace it but they were expensive. As it was someone else's dog I'd be going down that route if they were paying.
The gorilla tape was only meant to be a patch up as we had a week left on our trip.
Like I said, its not pretty and looks like it was thrown on(because it was) but it actually worked quite well so we decided to leave it.
We repaired the mesh window in the lift up roof of our campervan with sticky tape, a few years back now, and it has held ok. As you say, not that pretty but does the job.
Could you not purchase some black netting from a hobby shop or curtain shop (you might be able to get fly netting on eBay) and then just sew a patch on with black thread? Might not be completely invisible but better than tape.
If you are away from home at the moment can you buy some black cotton and just sew the hole like fishermen do with fishing nets?