"walking" your cat?

I was wondering if anyone ever puts harnesses on your cats and takes them for a walk? I have three cats and my Oliver is very friendly and most tolarent when it comes to the harness. He will let me put it on but once I get him outside he freaks out about the harness and tries to run back into the house. How can I get him and my other two use to the harness they love staring outside? I would love for them to be able to roll around in the grass but I worry about them being safe hence the harness leash. 

One of my hubby's relatives does walk their cat outside on a leash with a harness.  His aunt told me that they first trained her indoors before taking her outside.  Perhaps this is something you could try,

If you take baby steps with your cats, they will probably adapt quite well to leash/harness wear.  Start out with short periods of wearing the harness indoors - praise and give treats.  Over time, lengthen the amount of time the harness is worn.  Then add the leash and repeat the steps.  Then step outside - only a minute at first.  After a few times outside at a minute apiece, start increasing the time.  Patience, praise and rewards!

My Pip is quite adventurous so for her outdoor adventures, we use a mesh pop-up tent (called a Happy Habitat).  She's fairly content to smell the breeze, watch the birds and the leaves so \i'm quite happy with it.  And with the tent, I don't have to worry about her getting tangled or caught up in anything.