As I said earlier in the thread, I think monks should only tank on a limited basis; probably at a ki/discipline/focus cost. They should be primarily skirmishers. But they still need the defensive capability to survive on the front line, and ideally that capability will fit the theme of the mobile, agile combatant.Again, this is skirmishing defense. It doesn't help the rest of the group. If the monsters can't reach the monk, they'll happily eat the wizard instead, and that's bad tanking.
If everyone in the group is trying to be in the second line, that just means that everyone is in the front line. The tank is the character who wants to be in the front line.
For when the monk does jump in to cover the tank role, movement reduction seems like the obvious way to do it.