If it's an Echotech they have/sell a thin black foam cover that goes around the PH preventing this from happening. If it's not an MP but close in size perhaps it would still work for you.
Try to keep several rocks between the Nem and PH that have multiple deep holes in them. This will help it grap hold and hopefully the Nem will find the right rock and place to call home. Reducing flow a tad helps while the Nem explores rocks. When it's moving around, it's not happy and looking for the right lighting, flow and perfect hole for its foot to attach in deeply. Once they find it, it will settle down and usually stay put unless you change their environment.
Sorry to hear about your Nem. This happened to me 4 years ago while moving. I broke down the tank & set it back up within hours and lost an MP cover in the process. The new placement, change in flow and lighting instigated Nem to move. It was a major MESS and took several large water changes to clear/correct the water. Just what you need while moving! The Nem was mangled but moved it to QT and it pulled through in a few weeks.
GL