sounds like hes coming on a treat, when i first had my terrier i bought her when she was 3, shes 6 now, but at first every hole she sniffed she wouldnt give a mark, in the end i decided to go against her nose and, geuss what she was right, but she didnt give a mark on so many holes that it got on my nerves, but there was just nothing at home, i changed area as to where i knew there was rabbits and low and behold , she 100% marking and has never let me down since, she'l hold the rabbit untill i get to it, bushes ect ect, in time your border will come on great, sounds like he's getting