Plane Sailing
Astral Admin - Mwahahaha!
I don't think defender lock-downs are bad; that is their job anyway, right? Besides, high level solos have such great stats compared to PCs they can take that measly -2 to attacks and still have good odds of hitting, and dodging an OA.
As I've illustrated with my quick tour of solo monsters above, most of the solos (once they reach high level at least) have ways of disengaging from fighters.
The "problem" that I've experienced is twofold really. The first is with fighters OA stopping movement and getting free attacks on marked targets who attempt to shift or damage someone else means that fights with solos suddenly get very static, which makes it a little less interesting.
The second part of the problem is that for the dragon, there is pretty much no option other than to rip the fighter apart as soon as possible in order that it can be free to attack other people again. As a DM I would sometimes like to spread the solo's attacks around a little to help keep the party as a whole alive; I can sorta manage that when there is a paladin marking it, but it is much harder when a fighter is marking it to find any reason to do anything other than take the fighter down as quickly as possible.
Now, that is allowing the fighter to act in a particularly 'defendery manner', sure... however, it can lead to a rather high turnover of fighters!
Cheers