Formula Query for Staff Rota

Hi

I wonder if someone could help me. I have compiled a staff rota from a website tutorial but have personalised it so I can use at our care home using a series of drop down boxes for each shift on each cell. What I would like is that so not to put someone on a night shift then a day the next day Excel alerts me (comes up red etc) so I can amend it as no one can physically work a night shift then a day shift the next day! This is a common error when doing the rotas and this would be great if someone could provide a solution.

Rota attached.

Thanks in advance

Bigtiger