As Jane has said, an 18 month age gap does not always ensure harmony - my parents' dogs also had more than a couple of years difference between them. They also got on fine with little sign of trouble until the younger one actually challenged the older - up to that point the older had been top dog with only the very occassional growl. The problem was that neither dog would back down once they started.
I honestly think it is largely down to luck how dogs get on with other. Most dogs living together get on fine all their lives, but now and then, you find a couple who just don't, whatever you have done - just like people really!
Have you considered neutering one (or even both) of them? I'm aware that this can be very hit and miss in terms of the affect on behaviour, but it is supposed to stop the marking in the house and may have a positive affect on the relationship between them. It also stops the humping!
I had a foster (aged 5) who was a humper and also had bad doggy manners (chin on shoulder, etc.) - Pip (neutered) would not tolerate his behaviour and things got quite nasty, Fletch (entire and a dog like no other) put up with it without fighting, but put a stop to it by playing him at his own game
- I found foster with a very sticky patch on his back
, which, just for information, was very difficult to wash off
. Foster was neutered and is happily living with another male cocker with no problems.
There is also the possibility that Jasper will grow out of his older teenage behaviour. Most do and if they are not fighting seriously, I personally would wait to see how it pans out.
Hope my ramblings help in some way!
Helen
