Yah, they are Shifty. He's shifting them all over the place. But when marked, it's still more of an advantage to target me, than the squishies. For one thing, I have Wardens Fury if they are in reach and Warden's Grasp if with in 5. So why take the extra damage.
You're playing a sword'n'board warden. An *adjacent* kobold that attacks one of your allies is likely to get decked with Warden's Fury, taking damage and granting combat advantage to your allies. A kobold at any range from you is going to be slid, slowed, and blocked from shifting until the end of it's turn as a reaction to attacking an ally. You only get one of those a turn, and it's a rare day when you're facing down a lone kobold.
Look, it comes down to the DM. If your marked targets are always attacking you, that's great. Focus on survivability. If the DM is constantly looking to get the kobolds past you and in to the squishies' faces (and succeeding), you might need to get tricksy in return. That's where Sudden Roots starts looking attractive.
On the topic of survivability... I agree that toughness isn't *bad*, but five HP isn't going to make a huge difference. You'd probably be better off taking Student of Battle (multiclass Warlord) as someone suggested to earn a daily minor action heal.
The other approach would be to switch out for a warhammer (or take a craghammer proficiency feat) and start dishing out extra damage through feats like Crippling Crush, Courage of the Lone Stag, and Crushing Guardian. "Slowed" may not inconvenience kobolds a whole lot, but "dead" will certainly put a dent in their shifty tactics. That also increases the odds that Markings of the Predator (already suggested) will actually trigger for you, increasing your defenses (it's still not a great feat -- it only triggers when YOU bloody a creature -- but it is an option to buff your defenses). Once you hit high heroic, a Hammer Shield (also suggested earlier) will boost your defenses further.