Why is my dog reactive on leash but perfectly calm off-leash?

Marc, quick question first: does Otto pull consistently on leash in neutral situations, like just walking around your neighborhood with no dogs present? Trying to figure out if the hardware itself is the trigger or if it's more the combo of leash plus dog stimulus.

Because those are actually pretty different problems. One is a conditioned response to the equipment, the other is more about the restraint amplifying frustration that was already building.

Loki had something similar early on. Slack helping but not reliably sounds like you're managing arousal in the moment rather than changing the underlying state. LAT is solid but if his baseline is already elevated before the other dog appears, you're starting behind.

Diego's point about baseline arousal is worth sitting with, Marc. From what I've read, leash reactivity often involves what people call 'trigger stacking,' where the arousal from wearing the leash compounds with the dog-stimulus before you've even registered a reaction. So the question of whether Otto is already slightly elevated just from being clipped in is a real one. Have you tried practicing the leash-on routine in a totally sterile environment, no dogs, no walks, just attaching and detaching repeatedly? Might help tease apart the hardware association piece.