When you apply to renew your PR card, you have to list your whereabouts in the previous 5 years so you should start keeping track of your travel dates right now. If you have been outside Canada for 1095 days or more, you fill out another section where you put down your excuses. One of the accepted excuses is that you are accompanying a Canadian citizen spouse. You can look at the renewal form here:
http://www.cic.gc.ca/english/information/applications/prcard.aspIf they ask you for proof, it would be good to have something like bank statements or phone bills.