To defend themselves against death from disease and prevent decline from accumulated damage, organisms must invest in immunity as well as repair. These defence systems are intimately linked: collateral damage of immune responses involves production of oxidative molecules while repair involves containment of resultant oxidative stress. Optimisation of defences is constrained by the need for organisms to operate as a single functional unit. I will identify what aspects of functional integration limit self-maintenance strategies of free-living animals and the consequences for senescence and longevity. The outcomes will provide insights into fundamental characteristics of animals that influence achievement of a long and healthy life.