You can also eat the young paddles look up nopales for more information. I am assuming you are looking at Opuntia ficus-indica. You have a lot of choices there from a "Burbank Spineless" to a man catching 3" evil spine producing version. Some other info. regarding Opuntia ficus-indica: Even the Burbank Spineless can produce spines just not many compared to others. Spine production appears to be a direct result of growing conditions, harsh sun being the most prominent. All of the Opuntia species will produce glochids however, glochids are evil hair like spines that you really don't want to mess with or get on you, they generally show up in spring and fall of by winter. You can burn the glochids off the paddles with a torch or toss them on the BBQ or similar to burn them off before use.
There is definitely an Opuntia available for just about every environment on the planet but some are much more cold tolerant than others. If you get a lot of cold do your research so you don't have mush come spring.
I think the use of cactus and succulents gets overlooked a lot so I do approve of your line of thinking just be conscious of giving plenty of space to move around, you do not want to brush up against a glochid covered paddle. If you are looking at the ficus-indica specifically you should know Luther Burbank created the spineless form for ranchers to be used as a feed in difficult times. He came to this from observing the diverse wild life that readily eats it and uses it for habitat so be sure about which type critters you are looking to keep out. You might be inviting more of them in. Rabbits in particular come to mind.
"Study books and observe nature. When the two don't agree, throw out the books" -William A Albrecht
"You cannot reason a man out of a position he has not reasoned himself into." - Benjamin Franklin
Opuntia grows very dense here. The native kinds grow low and dense, usually only a couple feet tall but four feet or more wide. "Spineless" cultivars grow 3 feet or taller though tend to develop a trunk at the base which will allow smaller critters through. I think a cactus fence is a great idea. Perhaps "Spineless" opuntia on the inside (garden side) with a row of low spiny opuntia on the outside.