Doctor Lindsay Hay, owner of Baulkham Hills Veterinary Hospital, has stressed that if ingested by dogs, Foxoff poison baits - which contain the chemical 1080, or "sodium fluoro acetate" - are incredibly quick-acting, and ultimately lethal.

"A dog would become acutely and dramatically ill very quickly after eating it, so it's not something that's going to happen the next day," he said.

"They seizure and they froth, and they die very quickly, within 30 to 60 minutes after they show signs.

"In areas where they have been affected by it, most dogs that present are dead because it's so toxic."

Doctor Hay said that domesticated cats are at a lower risk of being poisoned than dogs, as they are less likely to eat a bait under the misconception that it's food and don't tend to gravitate towards bushland.

But, the substance would still be highly toxic to the animals if it were ingested.

"It's normally not treatable," Doctor Hay said.

From Monday until October 12, the Hills Shire Council and the City of Parramatta Council are planting the poison baits in Bidjigal Reserve, the Excelsior Reserve and the Ted Horwood Reserve in Baulkham Hills; the Eric Mobbs Reserve in Castle Hill; Lot 51, Cadwells Road in Kenthurst; and, Lake Parramatta Reserve in Parramatta.

While dates haven't been set as yet, fox baiting will also be carried out in Sydney's south-west in areas throughout Macarthur including the Oaks, Oakdale, and Orangeville during Spring. The upper Hawkesbury region will also be targeted, with the Yarramundi, Grose Wold, Kurrajong Hills, Glossodia, Mellong and Freemans Reach among the areas to be baited.

Residents are advised to keep an eye on their mailboxes to be notified of each program's dates and the specific reserves that will be focussed on.

The baits will be buried to reduce the risk of non-target poisoning, and warning signs will also be displayed to notify the public about the program.

Both the Hills Shire Council and the City of Parramatta Council have warned pet owners to take extra precautions and avoid the local reserves that will be treated from Monday onwards.

If they do enter the reserves with their pets, before it's safe to do so on October 13, owners face penalties of up to $1100 under the Local Government Act.

"The fox baiting program has been going on for years and years. They [councils] always let vets know when it's happening," said Dr Hay.

"In all the time they've done it, our vet has never had a case of a dog ingesting it, so the risks are incredibly low it seems. This is mainly because of the way it's handled - the signs and the warnings."

Monday's fox baiting program comes just weeks after Ryde residents erupted in a flurry of concern after a fox "the size of a labrador" was spotted crossing Victoria Road with a chicken in its mouth.

In response to the incident, the City of Ryde council told the Herald that, like the Hills Shire Council and the City of Parramatta Council, it has an ongoing program to control fox populations. The programs are run twice a year across Sydney's council districts, in autumn and spring, and have a duration of about six to seven weeks.

But they do not extend to urban areas, where restrictions are in place on private lands.

This makes controlling Sydney's populations harder, as these areas often offer an easy source of food for the animals.

Greater Sydney Local Land Services Biosecurity Manager Graham Wilson said that residents can take a couple of simple steps to help keep foxes out of urban areas.

"Residents can help by enclosing compost bins, keeping rubbish in a secure location, feeding domestic pets inside and, wherever possible, keeping them in overnight," Mr Wilson said.

"[We] receive complaints about foxes killing domestic animals, including backyard chickens and guinea pigs."

According to the best available estimates, fox density in urban areas is about 10 per square kilometre. The animals are estimated to cost the Australian agricultural sector about $28 million every year.