At 7 months old your rottweiler walked past other dogs on a flat collar. At 14 months old they weigh more than you can hold. A lunge toward the road has stopped being a nuisance and started being a risk.
You are not the first owner to get here, and it is not a sign that you raised them badly. Strength arriving faster than training does is the ordinary shape of a large adolescent dog.
What changed
Two things moved at once. Around the onset of adolescence, dogs respond less to the cues of the person who raised them, and that responsiveness returns later in the stage.
On top of that, your dog grew. The pulling habit did not get much worse. It got heavier, and the same habit at twice the weight is a different problem.
Treat this as a safety question first
Be honest about what you can hold. If you are not confident you could stop your dog reaching the road, the walk is a safety risk rather than a training session.
Shorten the route until you can manage it. A 10 minute walk you control teaches your dog more than 40 minutes of being towed.
Change the time and the place. A quiet street at 6am is a different walk from the park at 5pm, and a fairer one to ask of you both.
Do not walk a dog you cannot hold toward traffic, livestock or children. Drive somewhere with a fenced space, or skip the walk today.
Equipment, and the reasoning behind it
A well-fitted harness with a front attachment point changes your leverage, so a lunge turns your dog rather than dragging you down the road. A front and a back clip give you 2 places to attach a lead.
Use a plain 6 foot leash in one hand. Never wrap it round your wrist, and never clip it to your waist.
You do not need a prong collar, a shock collar or a choke chain, and the reason is not squeamishness. A review of aversive training methods found them associated with worse welfare outcomes and no training advantage.
Dogs trained with aversive methods showed more stress-related behaviour than dogs trained with rewards. Punishment-based approaches are associated with fear, avoidance and defensive aggression. That is the whole case, and there is no trade-off to weigh up.
Build lead skills you can physically keep
Work somewhere boring, with 20 small treats in your pocket. Feed 1 down by your leg every 3 or 4 steps while the lead hangs loose.
Stop when the lead tightens, and wait. The moment your dog eases the pressure, feed and walk on.
Keep the criteria small enough that your dog can meet it 4 times out of 5. Stay below the level that pushes them past what they can manage.
End every session while the lead is still loose, not after a failure. 5 good minutes beat 25 bad ones.
Pay the check-in. A glance toward you on a walk is what makes everything else possible, and it costs 1 treat.
Reward-based training has been associated with higher reported responsiveness and fewer reported problem behaviours.
Give the strength somewhere else to go
Behaviour change is built from management plus reinforcement together. Management is the walk you can actually hold. Reinforcement is the skill you build between walks.
Trade some of the pavement for sniffing on a long line in a safe space, where pulling puts nobody at risk.
Practise a settle on a mat at home. Relaxation is trained as a behaviour in its own right, in short repeatable sets below your dog's threshold.
Use food puzzles and chews on the days the weather or your shoulder will not let you walk the dog you have.
Safety note
A dog who suddenly starts pulling, lagging or refusing to walk is worth a veterinary examination. Pain frequently presents as a change in behaviour rather than as obvious lameness, and a fast-growing large adolescent can be sore rather than reluctant. Get help now if your dog has pulled you over, or has growled at, snapped at or bitten a person or another dog.
When to bring a trainer in
If you cannot hold your dog today, do not wait for the skill to catch up. A trainer or behaviourist who works with reward-based methods can look at your handling, your equipment and your dog. They can give you something you can physically do.
Our article on choosing a trainer sets out what to ask, and what a good answer sounds like. Nothing written here is a substitute for a pair of hands that can hold the dog you have.
What to expect
Nobody can promise you a rottweiler who never lunges. A harness that turns a lunge instead of dragging you, shorter routes, and paid loose leash practice are what get closest.
If the strength is one of several adolescent things at once, the Assessment will sort which to work on first. It is free, takes about 3 minutes, and asks for no email address.
Tonight's version, in one line: check the harness fit, move the lead to the front clip, and walk 5 paid minutes somewhere quiet.