Hi - had similar problem with ds1. Dry just before he turned 3 - but he was seriously with-holding poo. This can cause long term medical problems so made a deal with him that he could wear a nappy to do a poo. This reduced his anxiety, taught him to acknowledge when he needed to go, tell me and hold back untill appropriate time. Then progressed to wearing nappy, doing poo in the bathroom, putting poo down toilet. Didn't ever push the issue coz we were having family problems too but we talked about where other people poo'ed when he instigated the conversation. Breakthrough came when one of his friends came round and pooed in our toilet and he thought it was ace.