Help with house training?

[Tyler]

i currently have a two year old border collie that i rescued over a month ago. he is not neutered which im am currently working on with pet over population. he is a very loving dog but skidish at times. the problem i am running into is he is the perfect dog when i am around. even when i go to work he has no accidents in the house, which he is by himself all the time. the problem is when he either gets extremely excoted or i turn my back for 5 min he will snatch food off the counter or rellieve himsellf, which is right in front on me about ten minutes he started pooping when i got him excited about taking a walk. he has been doing this a lot lately and i want to help him understand the difference between when and where to go to the bathroom. at times we will come out of a convience store on a walk and he has well piss and shit all over the place. he is a pure breed border collie and i know he is smart and a great dog. i just need some advice on why he releases himself when he gets so excited rather than do so when i take him outside.