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 ω -stable NDOP theory for which every expansion by a linear order interprets pseudofinite arithmetic.