You have to be joking. I could never go anywhere on my own without a full explanation, even to the shops. To be fair she always used to tell me too, but she allowed herself a lot more flexibility on stopping for chats etc than I had. I've had friends wives occasionally ask me things which show they are clearly checking up on their OH. My wife used to check the mileage on my car and make a list of where I said I had been, and compare the two. She left her diary open on the bed one day and I wondered what all the strange figures were and then the penny dropped. And that was when I was not doing anything she wouldn't have approved of. She also sometimes asked neighbours what time I went out and returned. It wasn't until one of them told me about it that I realised what was going on. At the time I was completely innocent. One day I told a close friend about it and he said his wife was very similar. We were very close for years my wife and I, but that kind of broke the magic and as soon as our sex life went into a lull she made sure it didn't recover.
What the fuck, she sounds crazy, checking the mileage on your car. I would be straight out of that one, even if I wasn't punting I don't want my other half so paranoid, eventually she will explode.
As for excuses, I can't say that i'm just popping out. Return about 2 hours later (1 hour punt, half hour travel both ways), the OH would be suspicious definitely, as for seeing friends and all that, we share a lot of friends. Only one I can think of would be watching the football with mates, but then you have to rely on your friends to not reveal the truth.
Always a working late situation for me, also make sure I stay in the office a while after work so I don't come home at 6 most days and 7.30 the next.