In my experience breaking concentration usually does not work the moment you need it the most, we couldn't break f.e. Nere's over two turns (despite 5 hits). "Dispel Magic" seems to be the possibility I'm looking for.
For the rest, I'm hoping for mods which change the combat more to 5e.
The cheapest way, beyond just attacking, to remove concentration is expose the concentrating target to a damaging surface. There is no save versus surface damage, and a single point of damage forces a DC 10 constitution saving throw to maintain concentration. Other than that, you can target their Dex with ice or grease surface, target Str with a Trip Attack maneuver, or target Wis with the Command spell (Grovel). All of which will render the target prone, immediately breaking the target's concentration.
Beyond that, it's best to attack with abilities or spells that the game considers multiple sources of damage. There will be a constitution saving throw for each source the game considers separate, though it's not always logical how the game decides this, you'll have to play around with them. Magic Missile would be a good example.
