We introduce ex-post participation constraints in a setting in which, repeatedly, two agents have to take a joint action, cannot resort to side payments, and each period are privately informed about their favorite actions. We derive a number of results. First, we show that, irrespective of how patient the agents are, any mechanism satisfying ex-post participation constraints delivers outcomes that are bounded away from efficiency. Second, for an agent whose outside option became tempting, the optimal mechanism (i) gives, relatively to a forced participation setting, less weight on current actions and, so to allow the agents to continue to trading decision rights in the future, (ii) always promises continuation values that are higher than the value of his outside option. Finally, we derive properties of the dynamics of relative bargain power, and prove that it leads to a unique limiting distribution of power. This limiting distribution is non-degenerate, memoryless and such that power continually changes hands in the limit, meaning that the weight agents have on decisions necessarily varies from period to period.