Surround your air defenses with spring traps and seeking air mines, best way to keep out giants. I've held off most giant attacks (TH 8), mainly since just about every giant-based comp I've been attacked with spawned troops in the exact same location.
I'm not sure how your base is set up, but just watch replays and if those attacking you seem to have a tendency to attack a certain side, trap that side up since it's likely they saw what they thought would be the best place to attack from. More likely than not another attacker will see the same thing.
Or, as others have said you could make a anti-hog type base to keep the giants walking in circles
Good luck!
