a bushing terrier roams free to put stuff up ,rat rabbitt squirell whatever,most terrier men i know aproach a earth ,with the earthdog on a lead or couples ,to firstly get a picture of the earth they are going to work ,if you let the earth dog run loose over earths or setts you loose the option of leting him enter only what you want ,i have know terriers that can do both jobs n do them well ,but there can be some scary moments along the way !!