In the modern day, fire managers dig or mow firebreaks to contain a burn. Did indigenous peoples do the same? There's a lot of literature out there on why they burned, and some information about to what extent, but I can't seem to find much about how they actually accomplished it?
From my viewpoint in the Northwest Coast Culture Area, a key factor was the timing of burning. In the North Coast Ranges of California, natives along the Klamath River and it's tributaries burned every year around their villages as soon as the grass dried enough so that the fire would burn the dry grass but not burn in the shaded areas under the surrounding forest canopy. Farther away from villages, natives burned in the Autumn when fires would usually be put out by the early rains. Burning in the fall resulted in "cool" fires that stayed on the forest floors and did not result in torching or burning the forest canopy. In the Puget Sound prairies of western Washington, the pattern was the same - burning extensively in the fall, often after some rain had fallen thus selecting for cooler, safer fires.
One thing that people need to remember is that prehistoric landscapes in the west were largely formed by native burning. Much of the forest structure was and had been shaped by centuries of burning. The resulting vegetation structure is not like we witness today after 100 years of National Forest anti-fire management. Environments shaped by natives had much more open short-grass prairies with younger shrubs. Many of the native-managed forests exhibited a park-like structure with large fire resistant trees with rugose bark (very rough bark up to six inches thick) and virtually no understory. Environments like these can withstand frequent burning, especially if it was timed correctly.
Finally, because the natives burned religiously around areas they wanted protected (e.g. villages and prime collecting areas), they really did not care about fires getting away from them.
Edit: I added a photo of the historic village of Weitchpec at the confluence of the Klamath and Trinity Rivers of northwestern California. Note the traditional plank houses closest to the river and how little vegetation there is between/among the houses and throughout the village.
Arthur R. Kruckeberg 1991 The Natural history of Puget Sound Country. University of Washington Press.
Pliny Earle Goddard 1903 Life and Culture of the Hupa. University of California Publications in American Archaeology and Ethnology.
