Spence I used to cut cement for a living....when they do road work they often cut the asphault before they dig a trench or hole...they use a saw that you push much like a lawnmower. The blade is a diamond tipped blade and is cooled with water.....tell the rental company you want a "wetsaw" with a blade big enough to cut what you want...probably you will need a 10 inch blade......provided you get this type of saw, you snap a chaulk line on your cut and you make several small passes each approximately 2 inches deep....this way your cut will not wander. Do it right and it will be clean and lazerbeam straight! Let me know how you make out.
