I have a lovely little Westie called Archie who is now 6 months old.  He has been very good with regards to toilet training up until the past week where he has urinated inside a few times.  This is very unusual for him and I am worried as to why he is doing this.  Can anyone provide any suggestions?  I take him to work with me every day and he goes for a walk 3 times a day and then in the evenings weather permitting.  He has become quite close to my parents Llhasa Apso and I wondered if he misses him.  This is the only thing I can think of.  Any suggestions would be appreciated.

I'd suspect he's approaching sexual maturity and is finding himself driven by hormones to 'mark' his territory.  MAke sure you keep an eye on his to distract him the minute you see him sniffing around, and if he does wee, that it is cleaned up with a biological washing powder solution, and sprayed over with white spirit to break down the fatty acids which hold the scent..........  It might also be worth taking a mid stream urine sample to the vets to make sure he's not suffering a urinary tract infection.