Hello!
Some clarification is needed to be able to help
1. Why you do not want to use HSRP or VRRP; this kind of redundancy is their purpouse
2. 2811 is your border router?
3. Gateway for your clients will be on the core routers? (I'm thinking that this is the correct way)
4. What routing protocol you intend to use between core sw and border router?
Cheers,
Calin