I'm going to get my greyhound a kong but not sure which size! [[http://m.mumsnet.com/Talk/the_doghouse/1477949-I-think-our-dog-howls-when-we-go-out-Not-sure-what-to-do This is why he needs one, hopefully it will work!]] I can't stand peanut butter or cream cheese so I don't buy it. So what else could I use to plug it up with?