I'm obviously just insanely fortunate to have a completely clueless OH, then. Well, "clueless" in the sense that she takes no interest in my financial activities.
Not at all complacent, and very careful with phone, etc (having had fingers burned in the past - nowt to do with OH). Just that my cash is mine, and so long as I pay my share to the household account, OH takes no interest in my personal spending. It helps that I have a "midlife crisis" vehicle, so I can use that as a reason for spending money if need be.
For me it's just about having peace of mind. As long as I pay the bills, buy stuff for her and take her out often enough, she doesn't complain, and as far as I know, she's not sitting around suspicious of me looking over my bank statements. She gets the illusion of being in a nicely clear and trusting relationship, so trusts me and gives me regular sex and pleasant companionship, which is what I want from her. But I can relax and still fuck prossies when the desire arises, knowing that if she did start digging around then she'd have a hard time finding things to question.
It's all about keeping up the pretense in my relationship you see... I want both my cakes and to eat them both. I could turn around to her and tell her not to look at my personal things, but that would very likely destroy a cornerstone of what makes the relationship enjoyable for me and probably for her too.
First few months when I started punting, I didn't take such precautions. I never got caught out, but I'll tell you what, it was a very unpleasant paranoid experience for me. But, at the end of the day, it's about taking the precautions that work for you. That will obviously be different depending on each punter's situation. For example, the midlife crisis excuse wouldn't work for me.. But it's a good excuse to have. Maybe in a few years I'll be using that one.