jquery validation, if condition

jquery validation, if condition

My form contains a label with 2 checkbox inputs (id=name, name = memtype), one of which is  'guide'.  I have memtype required in validation rules with an appropriate message for failing to check a box. 

I also have another text input (id=sponout, name=sponout) that MUST be filled in IF memtype = 'guide'.  How may I set a rule for this 'if condition' so that if a user checks memtype 'guide', but don't enter text in sponout, they receive an error message?