Officers in parts of Washington state have either attempted to retrain their animals to ignore pot or, for new police dogs, taught them to smell all narcotics other than cannabis. In other states, agencies have kept their pot-sniffing dogs and continued to search for large amounts of the drug not allowed under the law, although a recent legal challenge could soon change that.
If I recall correctly, most K-9's are bred in Europe and go through a lot of expensive training before joining a precinct. I can understand the idea of someone seeing that as wasted now.
So...utilize the current K-9's and just don't arrest someone with small amounts of pot. Then upon entry, don't have the new k-9's trained to sniff it out.
The money is spent, don't throw it out, just don't spend it again next time.