Never been on here before but hope that someone can help us

We rescued Duke our Collie cross 3 years ago & we believe he is roughly 9 years old now, in Jan 09 we introduced a puppy Rottweiler called Keisha. Both got along fine, they spend all day & night together in beds next to each other. However, after the evening walk & feed Duke will always return to his bed &  Keisha will roam around chewing her bone, chasing her tail etc. As soon as she goes even remotely close to him or generally looks in his direction Duke immediately starts manically barking, baring his teeth & looking generally very agressive. We know that they get on well together as they play together on the walks but we just can't seem to get him out of this mindset. We know he is an amazing dog but just seems to be isolating himself

Any suggestions would be great

many thanks

Could it be that Duke feels he HAS to be that 'assertive' in order for Keisha to pay any attention to him? ie, Rotties & collies have a completey different persona and a rottie will be much more 'rough & tumble'/full-on, it may be that subtle hints from Duke, telling Keisha to stay away (as he wants his peace & quite, not any of that silly puppy-nonsense), are getting ignored or are not 'enough' for her to pay attention to.

I am not vastly experienced in multi-dog households, but I do know that when I brought my mastiff puppy home, my older dog (lab cross) really had to act nasty in order for the pup to pay any attention to him. There was never any blood shed, but the old dog really looked & sounded mean when ever he wanted the pup to leave him alone, as the general ignoring (head turned away) was just lost on the Mastiff pup.

Hope somebody will be along soon to offer some suggestions.

Most probably she has tried to cuddle up with him and her being such a lump has nearly crushed him. He may also feel safer to tell her "keep back" when you are about rather than night time when no one is there? My lot would love to have a mad 5 minutes play after tea but  now my oldest boy is 10 yrs does not par take anymore yours  being 9 is getting on a bit now so most probably feels the same he would rather have a snooze after his tea I know I do lol