[colicoid]

AND; don't use due dates for this. Due dates should be reserved for "hard dates". A hard date is when something needs to be done before that date or something nasty will happen (send in taxes, pay phone bill, give report to Boss before he goes on vacation etc.).

As an option to repeating task for "practice my guitar" you could simply set a start date for the next time you think you will be able to / want to practice. When that day comes the task will reappear (filter set to available) and you can then choose whether you want to do it or not.

Remember that tasks that don't have due dates should be optional as much as possible. You can do them or you can safely choose to not do them. Don't look at your task list as something that you "have to do" but something that "you could do if you feel like it". This should reduce some stress for you...