As long as you are with your husband and he is a citizen and you are a PR, you can not lose your PR status.
The 5 year periods are not counted as period one August 2003 to August 2008 and period 2 August 2008 to August 2013. It is a rolling 5 year period. You have to meet your residency requirements always in the immediate 5 years previous.
With an expired PR card, when you want to go back to Canada, you need to apply for a PR travel document, see
http://www.cic.gc.ca/english/information/applications/travel.asp and to apply for this documents, you need to list all your absences for the previous 5 years before you apply.