Indoor asset tracking is an essential task in many areas of industry such as shipping and warehousing. Widely-used asset tracking technologies typically require supporting infrastructure (signal transponders) to communicate with active tags on the assets. Continuous asset tracking in large indoor spaces like warehouses can be costly, and reliable reference points are needed to calculate asset positions accurately. In this paper, we describe an indoor asset tracking technique for augmented reality (AR) that combines the use of (passive) fiducial markers together with flexible spatial anchors. Our approach, called SABIAT, continuously tracks the approximate location of an asset using spatial anchors and, when needed, the precise location of that asset using fiducial markers. We have applied our SABIAT technique to build a demonstrator system, AR-IPS, to show how assets can be tracked and located inside of a large, multi-level building.