Cisco :: IPS Inside Or Outside FW?

Been reading up on IPSs some and some sources say the IPS goes inside the FW some say it goes outside. I know the inside is easier to tune and more secure, what are ya'll's oppenions on where it should go and why? (I will say most of them say IPSs on the inside and outside, but I figure that's something of a marketing ploy)I kinda like inside the FW to keep it a bit more safe and to avoid the stuff the FW will kill by default that's out gunking up the internet.