My simple precautions were a seperate hobby phone that's pay as I go, stays in my car and is registered at 1060 w addison st in chicago (wrigley field)

Seperate gmail account under an alias (actually it's under my boss's name because he's a dick and I found that funny)

And of course have a good story to account for your time.

But no matter what you do there's a decent chance your SO isn't an idiot, and will suspect something. In my case the relationship ended for other reasons than being caught, but she suspected something because I was happier than usual, went through all my e-mail and phone records, never found the hobby stuff.

Now I hobby just because it's fun. Still have the e-mail and hobby phone, just don't have to make up stories anymore.

There is no reward without risk, you can minimize the risk by not being stupid. And only you can determine if the reward is worth it.