When my lamium gets leggy (usually about when the blooms are fading), I cut it back to about 1-2". It recovers quickly. I have two cultivars, both in the L. maculatum family - Chequers and White Nancy. Chequers is more aggressive about colonizing, but is easy to pull where I don't want it. I use both for reblooming jolly little groundcovers. I think L. galeogdolon (yellow lamium) may be more aggressive in general, but not really sure. My son has it pretty much overtaking an entire shady side yard.