Thought I'd post this as ,in the past, getting door liners to stick back on has proven difficult.

I haven't been able to find any posts on this, so I don't know what every one else is using, but I just picked up some 3M 9415pc double sided tape. It is very sticky on one side, not too sticky on the other. Put the very sticky side on your car, and the not too sticky side is great for sticking the thin plastic door liner back on. The door liner will peel back off without ripping, and then it will re-adhere to the tape.

Thanks for the tip.