Sticky back velcro. I have 2 laminated A2 posters that would not stay on the wall. I bought a strip of sticky backed velcro and it's worked a treat (the strip was better value than the dots).
I have a certain spot on my wall that nothing I've tried works! It's right above the chalkboard, where my alphabet line is, DEF are on the chalkboard. I've used many, if not all of the ideas suggest here, except for the painters tape. I may have to try that one!
