The long propagation delays of the underwater acoustic channel make traditional Medium Access schemes impractical and inefficient under water. This paper introduces and studies Interference Avoidance and Network Coding for Medium Access protocol design aiming to cope with the underwater channel constraints and achieve efficient data transmission under water. Network Coding can exploit the broadcast channel to send different information to several receivers simultaneously. With Interference Avoidance the long propagation delay can be used to communicate in full-duplex mode. Alone and combined these concepts could increase channel utilisation as well as improve energy efficiency of the network nodes. The main goal is to investigate the potential benefits of new strategies for data dissemination over a string topology scenario. Comprehensive simulations prove the feasibility of Interference Avoidance and Network Coding improving the system efficiency when compared with CSMA/CA.