So did I.I use SKS Raceblades. Just make sure you put the frame protector tape on to stop grit getting underneath and scratching the frame. I learned the hard way!
What about the dedicated Giant defy guards if you can find them?I’ve just got hold of a giant defy from 2014. Mint condition only 200 miles according to the seller (and I believe them). The callipers are short drop and don’t look like the take full guards. The frustration is, the bike has dedicated mudguard fixing points. It looks like I will have to for for raceblades longs.