Supermarket spot-on failed? Better flea treatment for dogs

If your supermarket spot-on has stopped working, you're likely dealing with flea resistance — it's genuinely common with over-the-counter treatments, and it means you need a product with a different active ingredient rather than just a stronger dose of the same thing. Here's the important bit though: treating your dog alone won't crack this. Around 95% of fleas in an infestation live in your home — in carpets, sofas, and bedding — not on your dog. A single product rarely handles both, so you'll need to tackle the dog and the environment at the same time. To point you in the right direction: what breed and size is your dog, how bad does the infestation look right now, and have you treated the home at all yet?

That makes a lot of sense — Golden Retrievers are heavy-coated dogs, which makes it easier to miss fleas, but six months of a supermarket product with live fleas still visible is a classic sign of resistance to permethrin or the older pyrethroids. At 32kg he's solidly in the large-dog bracket. Can I ask: are you seeing fleas jumping off him in the house, or mainly spotting them when you comb through his coat? And is he scratching a lot, or does he seem relatively unbothered?

Right, so you've got fleas in the environment already — that sofa sighting confirms it. For your dog, I'd move to Frontline Tri-Act for Large Dogs (20–40kg). It uses permethrin combined with fipronil and pyriproxyfen, but crucially the Tri-Act formulation adds a repellent action and kills faster than standard Frontline — it's meaningfully different from what supermarket products contain, and it's a proven vet-recommended prescription-free option. For the home, you need a household spray with an IGR — an insect growth regulator — that stops eggs and larvae developing. Indorex Defence Household Flea Spray is the one I'd reach for: it kills adults on contact and the IGR protection lasts up to 12 months. Vacuum thoroughly before you spray, wash his bedding on a hot cycle, and treat every room he goes in, not just the living room. Do both on the same day for best results.

One thorough treatment with Indorex is usually enough because of that long-lasting IGR — but you'll still see some adult fleas hatching over the next 2–3 weeks even after spraying, because the pupae stage is resistant to insecticides. Don't panic when that happens; it doesn't mean the treatment failed. Keep vacuuming regularly (it triggers hatching so they emerge into the treated environment) and make sure your dog's spot-on is applied on schedule. By week four, if you've treated both properly, you should be through the worst of it.

Yes, it's safe for a healthy 5-year-old dog — Frontline Tri-Act is licensed for dogs from 8 weeks and there's no upper age restriction for a dog in normal health. No prescription needed either; it's a POM-VPS product in some formulations but Tri-Act is available over the counter and you'll find it on Amazon UK without any issue. Just make sure you're buying the 20–40kg pack for his weight. If he has any skin conditions or you're using other medications, worth a quick word with your vet, but for a typical healthy Golden Retriever you're absolutely fine to go ahead.