Jack Russell aggression toward new dog: crate strategy

A Jack Russell with a new dog in the house is a really common flashpoint — JRTs are territorial by nature, and without a clear separate-space strategy the tension can escalate fast. Crate training works best here when each dog has their own crate that feels genuinely safe and theirs, not just a management tool. The right crate size, placement, and how you introduce it all matter more than most people expect. To point you in the right direction: what's the new dog's breed and age, are both crates starting from scratch or does the JRT already have a crate, and is this setup primarily at home?

That's a classic size-mismatch situation — a confident adult JRT and a bumbling Labrador puppy who doesn't yet read warning signals. The snapping is the JRT telling the puppy to back off, which is normal communication, but it can become a habit if they don't each get a clear retreat space. Before I get into the crate itself: where in the home are you planning to put these crates — same room, different rooms, or are you open to either?

Same room can work, but placement is critical — you want the crates far enough apart that the JRT doesn't feel the puppy is encroaching, ideally with crate doors facing different directions or a visual barrier between them. At 2 years old and never crated, your JRT will need a slow, positive introduction, so a crate with good visibility and ventilation helps her feel less trapped. The Lab puppy will need a significantly larger crate given how fast he'll grow. For both dogs, I'd go with the MidWest iCrate — it comes in multiple sizes, has a divider panel so the puppy's crate can grow with him, folds flat, and has a solid track record for anxious or reluctant first-time users. For the JRT, the 24-inch size is right. For the Lab, start with the 42-inch with the divider in place. It's straightforward, sturdy, and not overwhelming in design, which matters for a dog building a new association from scratch.

Separately, and don't rush the JRT. Start by just leaving the crate in the room with the door open and feeding her meals near it, then inside it over several days — no closing the door until she's relaxed going in on her own. The puppy will adapt faster, but don't let the puppy near the JRT's crate at all during this phase. That crate needs to be the JRT's space completely. Once both dogs are comfortable in their own crates, you can have supervised time where both are crated simultaneously in the same room. That parallel calm time does a lot for reducing overall tension between them.

Keep the JRT's access to the puppy short and structured to start — three to five minutes of supervised interaction, then separation before either dog gets overaroused. Give the JRT an exit route she can use herself, like a baby gate she can jump over but the puppy can't. Never punish the JRT for growling — it's communication, and removing it just removes the warning. As the puppy learns to read her signals and the JRT builds confidence that she has her own unchallenged space, the aggression usually reduces significantly within a few weeks.