2.9 DS won't wear nappy... or pants

[biggest]

We have been trying a laid back approach to potty training for a few months now, at first all was well and DS used potty for pee only but did not seem ready to give up nappies.
Then he progressed to stripping off his nappy when we are at home and refusing to wear pants (that he chose himself, tried that one!).
Now is naked and pee-ing with abandon where he likes as we have lost all control of the situation!
To complicate matters, his baby sister has just been born...
I would happily back off for a month and try again, but he can strip off his nappy in seconds so we are stuck between a rock and a hard place. Plus, he fiddles with himself constantly !
Please help! I dread having visitors as between this and my stupendously leaking boobs it is chaos