I'm also using a melee DPS {enhancement shaman} with mixed casters. I don't really run into many problems that chain heal can't fix. I try to keep my melee toons facing each other, since you generally want your melee DPS attacking a mob from behind, so I can usually just pull my tank and shaman apart. That is, my tank strafes left, my shammy strafes right, or they both back up in opposite directions. Follow breaks on melee combat, so the shammy will just stand there until I call her back in.