Adding linear orders
  We address the following question: Can we expand an NIP theory by adding a linear order such that the expansion is still NIP? Easily, if acl(A)=A for all A, then this is true. Otherwise, we give counterexamples. More precisely, there is a totally categorical theory for which every expansion by a linear order has IP. There is also an \omega-stable NDOP theory for which every expansion by a linear order interprets bounded arithmetic. 
Saharon Shelah, Pierre Simon
math.LO