I think its possible to pad the duty cycle pot so it doesn't.Square wave oscillator with both duty cycle and frequency adjsutments. Note that the adjustments probably interact with each other.
You can certainly minimize the duty cycle pot affecting the frequency by making the duty cycle pot much smaller than the frequency pot. For example the duty cycle pot could be 10l while leaving the frequency pot 500K. The maximum frequency shift resulting from changing the duty cycle would be (off the top ofmy head) about 1% (orI think its possible to pad the duty cycle pot so it doesn't.