On my 456 I used a regular fender ("mudguard" round these parts, but everyone knows what your on about). For the chainstays, I drilled a hole each side of the fender and put a cable tie thru the holes, round each chainstay and tensioned them against each other. It's rock solid, doesn't rattle and looks okay. I was having extra bottle mounts brazed on by a framebuilder anyhow, so had a single mount brazed on at the bottom of that short fat tube that runs to meet the seat stays and attached the fender at the top there.
There's a 101 ways to bodge a mudguard, I seem to have to do it in someway whatever the bike.