We have used this tactic with Morgan a lot recently. As many two year olds do (maybe mine more than others), Morgan likes to do things over and over...and over again. Lately after a healthy number of repeats we say "one more time." Then when she finishes that time, we say "all done." This has worked pretty well. It cuts down on the number of times we read a particular book, sing songs or play a tickle game. She seems fine with it when we say "all done" and moves on to another activity.
Today I was helping her jump on a pillow (she usually tries to jump on me, but we've managed to redirect that to a pillow now). After the second jumping session she said all by herself "one (more) time," then jumped for a little while, stopped, said "all done." Then she got down off the pillow and walked away. I didn't mind her jumping a little more and sat there a little puzzled when she went off to play with her kitchen. I just shrugged my shoulders and thought to myself, "OK, I guess she's done." Then I just had to giggle a little.