As an aside to your question I note that your parameters do not seem to be arbitrary. Can I suggest enumerating them, i.e. 0 for none, 1 for yes, 2 for no, 3 for yes and no.

The benefits of this are 2 fold... firstly you won't have to use URL encoding as it is guaranteed there are no spaces and secondly it will be harder for an individual to tamper with your URL as parameter meanings will be less verbose- how important this second point is depends on your view of security/purpose of the script.

If you create two subroutines: enum_param that takes a string (e.g. yes) and returns the number representing it and decode_param that reverses this. These will make it easy to use this process in more than one script.

Its only a thought and in many cases it might just be easier to URL encode. Hope it helps.