Linksys BEFW11S4 Issue

[MoFunk]

OK I had a netgear router running for the last couple of years and all was well until it just decided to burn up one day, so I bought the above mentioned router. Now I am having an issue with it! I have only had it a week and an ready to toss it! I have it set to forward some ports and I have dyndns so I can access my lan from work. Well whenever I go into the router to change ANYTHING, it gets a new ip address. This totally kills the connection and if I am at work, I have no way to update dyndns until I get home. Anyone know what setting that I am overlooking that will get this darn thing to keep it's ip? Thanks.