The following quote (from here) is probably a pretty decent bit of text to slap on the bottom of any contract an employeer of yours gives you regarding intellectual property rights:

Hobby Programming Waiver. The company waives all intellectual property rights to computer programs which (a) the employee produces on [his] own time and initiative with [his] own materials and equipment, and which (b) do not incorporate or contain the company's intellectual property, and which (c) would not appear in the eyes of the company's customers as replacements for, or equivalent alternatives to, any of the company's products or services which the employee helps write during [his] employment with the company, and which (d) the employee does not incorporate or include in work [he] creates for the company.

The only thing I worry about is, "contain the company's intellectual property". There's a temporal aspect to that bit that makes me wonder if you're going to mobius strip yourself into something nasty. "All you write belong to us; you write something at home; your new app includes IP you learned here; your new app belong to us." Hopefully (a) covers that well enough. I think the intent is clear to anyone reasonably well functioning.