Coordination　tracking　problem　of　multiagent　systems　is　studied　for　the　application　of　threat　defense　in　a　monitored　area.　When　targets　intrude　this　area,　agents　which　are　nearby　to　them　are　set　to　track　the　targets.　Modified　nonsingular　terminal　sliding　mode　controller　is　proposed　for　the　agents.　We　design　a　novel　continuous　function　in　the　controller　to　eliminate　the　singularity,　which　makes　it　able　to　estimate　the　finite　tracking　time.　Based　on　the　estimated　time,　generalized　Voronoi　diagram　considering　the　velocity　of　second-order　agents　and　targets　is　presented.　During　the　tracking　process,　the　event　of　node　failures　will　trigger　a　designed　coordination　strategy.　The　event　that　the　target　enters　a　new　generalized　Voronoi　cell　triggers　active　replacement　coordination　strategy.　With　the　proposed　active　replacement　strategy,　the　tracking　time　is　reduced　even　under　node　failures.　Comparison　lemma　is　utilized　to　deal　with　the　agent　switching　issue　caused　by　node　failures　or　active　replacements　under　new　event-triggered　coordination　strategies.