This paper offers a novel analysis of the complex patterns of exponence exhibited by the Somali subject marker (MRK). Somali subject marking presents a typologically rare case of subtractive grammatical tone in which an otherwise regular process of High tone loss is sometimes impeded or otherwise influenced by factors related to word structure. In the simplest instances, MRK is realized only tonally by the loss of High tone from the last word in a DP. Under some conditions, however, it is realized only segmentally, with no High tone loss. Still other times, both exponents appear, and even in a few instances, neither is realized. Though these outcomes are predictable, analyzing them presents several challenges. One of these is motivating the outcomes from a single underlying form given the apparent independence of the tonal and segmental exponents. Others concern defining the trigger of subtraction and the domain or valuation window in which subtraction occurs. We propose a formal account of these outcomes within Cophonologies by Phase (Sande & Jenks 2018; Sande, Jenks & Inkelas 2020), whose division of vocabulary items into three types of phonological content is uniquely suited to addressing these analytical hurdles.