cat gets stressed out in car

[honeybee4]

I took Mocha to the vet this morning for his snip snip. He was so stressed out. I put him in the car carrier and then when we got into the car he was foaming at the mouth and panting. The vet is only about a 5 to 10 min drive from our home depending on the traffic. Just before we got to the vet, around the corning, he got the dirrahea and peed all in his carrier. I felt so bad for him. I got him out of the carrier and cleaned him off with a towel that I had in the car and took him into the vet. I just called them and he is now doing great sitting happily in a cage awaiting his surgrey. How can I make his drive home less stressful and without the mess. I have to go and clean my car today it sticks of car urine and poo from him this morning even though he was in the carrier.