I think a woman always knows even though she may say nothing. It doesnt have to be smell, it can be mannerisms, your look, the way you act/talk.
Best tip,,have a punting outfit,change into it,,punt,,change out of it,shower,,,find a job around the house/wash the car so that you can wind down and when she comes back it makes it look like youve been busy and also puts you in the right frame of mind to be acting that role i.e the busy diy'er,,rather than someone who has just got their dick wet.