I have a boarding kennels(Dogs) and the expansion gap material has been dug out
Over time and I would like a better solution when repairing.

Here are some sealants:
Sika (http://www.homedepot.com/webapp/catalog/servlet/ContentView?pn=BP_Sika&storeId=10051&langId=-1&catalogId=10053)

You have a unique situation though as it sounds like the animals are digging the material out of the joint. One problem is that these sealants are designed to stay flexible so they can expand and contract. One question I would have--is that definitely an expansion joint or was it just a construction joint as the concrete was placed in small sections? Or maybe a joint that was sawed after the concrete had hardened to control cracking? Does the concrete abut anything on the sides? Unless it is "locked in" between two rigid structures, I would consider placing a backer rod (round flexible foam like strip) into the joint as far down into the joint as I could force it- then fill in the top of the joint with cement grout, to deter the digging by the animals. If it definitely is an expansion joint and must be kept flexible, you could consider placing a T shaped plastic molding over the joint after the flexible sealant is placed so that the bottom of the T is anchored in the sealant. Sounds like you have some hounds in that kennel. They are digging specialists. Good luck.