Yes, I use a cat harness and a lead with the Tobster - coming walkies with his meowmy is his party piece, he's even done it in the High Street here in Ely.
He has a german cat harness, can't remember the brand, but it's got the snap fixings as opposed to buckles (easier to get cat in and out of harness). I just use the standard lead that came with it and it seems to work fine.
A friend of mine has a harness called a "Walk n Vest" which also works quite well.
Have attached a photo of Toby with his lead and harness and sitting in his favourite basket during a CP fundraising event.
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