Eos is an environment for building distributed object-based systems. Leos, the language for Eos, provides transparency for distribution and persistence. In this paper, we address the problem of declustering the object graph into a number of nodes and of locally clustering objects within pages with minimal impact on the programming process. We propose a grouping model which on the one hand achieves full transparency. The grouping is dynamically achieved by the run-time system as directed by user-provided hints. This dynamic object grouping copes automatically with evolutions of the object graph. The implementation incurs little overhead it is a side-effect of garbage collection. On the other hand, our model supplies Eos users with an explicit and fine control over data and computation placement so they can load balance the overall system.