what is the best way to fix felt to an 8x6 shed roof?

Clout nails are simple and effective. You can get then in any diy store, they have a large soft head

If your any good with torch on felt then use it, it will last a lot longer than the normal shed felt, mind you dont set fire to your shed. An easier option is fit an epdm rubber roof glued to the boards, you can buy it to size, no joins, faster to do, no naked flames. PK1, EPDM £6 per square metre is cheaper than felt, how many roofs are you doing for £600 Try reading the question, he doesnt want to use nails and asked for alternatives, perhaps thats the only way you know how to fix felt.

You can get cold roll on felt if you don't want to torch or nail. However if you do use enough clout nails it shouldn't blow off.

rubber roof ? epdm its a shed roof BJD i dont suppose they have a spare £600 for the materials. Clout nails and green mineral will suffice.