Sometimes radar targets cross and become unresolved; this is a concern, but with a reasonable track depth and
an appropriate merged-measurement model the concern is considerably mitigated. Sonar targets, however, can
become merged (in the same beam) for considerably longer, particularly with bearing-only measurements. In
such cases the crossing times can be 100 scans long, and no reasonable depth exists for an multi-frame tracker
that can "see" both ends of the merged period. Further, there is a demonstrable tendency for estimated targets
to repel each other as they are being tracked. In this paper we explore the hypothesis-oriented multi-hypothesis
tracker (HO-MHT), an MHT approach that uses the new "rollout" optimization insight and the to give an appropriate and
cost-effective means to rank hypotheses, and also the PMHT tracker that operates on batches of scans with linear computational complexity in most quantities. We show results in terms of estimation error (RMSE), consistency (NEES) and computational effort in both linear and beam-space tracking scenarios.