There's more nonsense written about training Rotts...Encourage aggression indeed - rubbish.If the dog (any dog,not just Rotts) gets over excited by the game and offers aggression it's a great opportunity to nip the behaviour in the bud.
Dogs understand play perfectly well.
Guard breeds attract a school of thought trainer that insists on the 'dominance' training being absolute.
Piffle.
All of my Rotts have been adults with aggression issues when I took them on.
Once they settle I play tug of war with them - my arm being a hot favourite for them to tug on.
Never been so much as scratched.Bruised occasionally but they always seem to know what 'ouch' means.
Romeo is one of the present Rotts here and he IS a VERY nasty piece of work with every one but me.
I don't take him for a walk - he takes me with my arm gently clasped in his jaws.Never so much as a bruise have I received from him.

Great to see so many reasonable replies already! I've always played tug of war with my BSD (not a Rottie but still a breed that's rumoured to be 'prone to aggression') - and I usually let her win. I don't see that there's anything wrong with it, as long as the dog has a reliable release command. It can be a great way to train impulse control if you teach the dog not to take the tug toy until you signal him to. (Murv, that's not aimed at your shy girl, btw - sounds like the last thing she needs is control work.)

But at the end of the day, it's just a game, and dogs understand that perfectly well. (Well, my bitch hasn't filed for world domination yet... )

I found letting Rupert win really helped give him the confidence to play tug. He was really heistant to tug at first but now he'll drag me round the garden growling his head off and shaking the toy until I either let go or tell him to release. Once he's won the toy he prances off with it and then tries to re-engage me in the game.

My Rottie mix and Border collie mix used to play tug quite a bit in the garden and sometimes the rottie would win despite being the most submissive and non aggressive dog you could find. I almost always let him win if we played tug, the expression of joy on his face when he got the toy was awesome lol.

Yes, they look so proud and pleased with themselves when they tour the field carrying the toy! I love to see that.

It was especially nice to see it in Wolf as he was always the lowest dog on the totem pole no matter what the situation. He never seemed unhappy about basically being a doormat but it was just nice to see him "win" something now and then lol.

I'd avoid playfighting. The JRT Loves it and is extremely careful with his teeth but as a result associates male visitors as Yippee someone to play fight with - not everyone's as enthusiastic. So I don't encourage it. Fortunately he almost equally adores a game of tug.

Edit: By "I'd" I mean just me personally.

I am not sure what you mean by "play fighting" so cannot comment, I never understand this term.

Playing tuggy with ANY dog of ANY breed is perfectly fine as long as you a) set the rules b) you teach the dog the rules and c) it abides by them! Simple.

Rotties like many bull breeds often prefer a tug to a ball, whereas the pastoral breeds tend to prefer the latter; and there are those who enjoy both but have a preference for one or the other.

Tuggy is great
It can be a great way to teach impulse control too if you do it well - like get them excited playing then stop the game and ask for a sit or something then play some more - so they learn to listen to you even when a bit hyper

http://www.deesdogs.com/documents/LoweringArousal.pdf

Look at Dees article, it is very good

I have always played tug of war and rough and tumble with my rotties over the years,

I agree all my rotties preferred tug games,

However when Bruce first came here, he didn't know how to play, I threw a ball at him, it bounced off his head and he ran and hid behind a bush he plays now, but it has taken a while for him to have the confidence. yet i still don't play rough and tumble with him, not because i am worried about aggression, he just wouldn't like it