I am getting pick up notices for PR cards within about 3 months. So, the first piece of advice to any permanent resident is, apply for the card, now.
A permanent resident who is outside of Canada, without a PR Card can apply for a "travel document" which is a single-entry visa that can be inserted in their passport (you cannot apply for a PR Card outside of Canada). For people landed less than 3 years it's a no-brainer application, but after that the residency determination makes it complex.
That being said, Chapter ENF27 of the Immigration Manual says that the presumption against permanent residence does not apply at a port of entry. If you can get yourself to a port of entry (by driving in from the US, for example), then you can satisfy an officer of your permanent residence. However, I would not advise trying to rely on this in any but the most exceptional circumstances.