Need some creative decorating ideas for an office

[AnOtHeRdIsNeYfReAk]

My boss of 10 years is leaving for another position and I would like to decorate her office on her last day. Its a bit of a tradition for us to do this and I'm looking for something very memorable.​

To give a bit of background she was on leave for 3 months a few years ago and we put a for rent sign on her office door, decorated the inside with cobwebs, spiders and fake dust, wrapped a police caution sign and a condemned sign around it, and posted messages on her wall. When she was out for surgery we covered one side of her wall in blue paper, pasted dozens of fish on it and wrote in the "bubbles" Welcome back, and added some messages like: "We were drowning without you", etc...​

I'm drawing a blank this time. Maybe its because I'm trying too hard to top anything else we've ever done. I don't want her (or us)to have to clean up a lot, so a lot of things I'd like to do are out. We do have several hours to do this -Probably about 16 hours and we have several hands to help out. Any ideas?​