Rat Terriers

Seeking some advice/solutions for excessive outside barking by beloved male rattie(9 yrs old) with no other negative habits except (somewhat recent) exessive barking at squirrels, and sometimes other larger dogs when on leash. Main concern is continued barking when out side in enclosed area (or inside when he can see then) every time a squirrel appears...which is cotinuous in our NC area at this time...once barking commences, it is hard for him to stop--just continues on if he "perceives" the 'squirrel' might be there... any thoughts about the use of a "bark collar" ( has worked extremely well on another, much larger, noisier dog in the neighborhood--who is just delightful & friendly--and does not bark at all wile wearing is collar!) Feedback, etc will be much appreciated so a good decision can be made for our beloved (but overly noisy!) rattie!

mine barks to, thats their character