They are, for many of WA's critically endangered mammal species, a last shot at salvation on an island continent that has become overrun with feral predators.
From Shark Bay in the north to Perup nature reserve near Manjimup in the south, they are an increasingly important part of efforts to safeguard wildlife that would otherwise stand no chance of survival.
Technically known as "compounds", they are more like inland islands or sanctuaries - fenced off from the outside world and, more specifically, the menace of cats and foxes.
Neil Burrows, the Department of Parks and Wildlife's principal research scientist, said WA's first sanctuary was created on Peron Peninsula near Shark Bay in the mid 1990s.
Since then their prevalence has grown in line with the understanding of their merits.
The department is now involved in three others, including at Perup, where authorities are trying to halt a dramatic decline in woylie numbers, and Nangeen Hill nature reserve, about 200km east of Perth in the Wheatbelt.
At Nangeen Hill, desperate efforts are underway between the department and the World Wildlife Fund to save a group of black-flanked rock wallabies.
It is one of the last vestiges of a population that was once predominant across the South West until the introduction of feral predators.
The jewel in the crown, however, is Lorna Glen - a sprawling former pastoral station in the State's arid heart where the department has established a sanctuary zone.
Through Lorna Glen, it is hoped 11 species that long ago disappeared from the area, if not the mainland entirely, will be able to flourish again.
Dr Burrows said the growing use of compounds reflected their benefits but was also a tacit acknowledgment of the fact that some pests were in all likelihood here to stay.
He said the department's other strategies for dealing with introduced species, such as baiting, fire management and culling, were crucial for mitigating the spread of pests.
Dr Burrows said some particularly vulnerable marsupials including malas, boodies and Shark Bay mice were simply not equipped to deal with the threat of feral predators. "It's recognition that if we want to preserve or protect some of our most endangered fauna this is an additional strategy for doing that," he said.
"There some species that simply cannot exist even with low levels of predation from these animals, so that's why we've had to go down the path of building these compounds.
"A lot of these animals that are going into and will continue to go into these sanctuaries only occur on two or three offshore islands off the WA coast.
"They were once abundant on the mainland but have since disappeared.
"So it's really an insurance policy - the more populations of these animals we can have established on the mainland, even in these fenced sanctuaries, the greater the probability is we will preserve them into the future."
Dr Burrows also flagged a greater role for the private sector and conservation industry in establishing more sanctuary zones in future, noting they had already provided important support.
The department's director of science, Margaret Byrne, said there had been criticism suggesting shelters amounted to nothing more than zoos but this ignored the scale on which they were being built.
"The animals are living as they would, it's just that the fence is there as a protection," Dr Byrne said.
Environment Minister Albert Jacob praised the sanctuaries as an important conservation measure, although noted it formed part of a broader strategy.