It really depends on what you would like to make redundant. IF you have a lot of closet switches (i.e. 3560 or 2960) connected - you could those switches with one connection to each of your 4503. Then on loss of a core switch or ONE of the uplinks, you don't lose anything IF you have servers with multiple links, you could attach one to each 4503 if the server OS software supports that - exact method depends on the server OS. Low tech / non-automatic way would be to have spare ports on either, and you can move all non-redundant connections to the OTHER 4503 if one fails.

It really depends on what you would like to make redundant. IF you have a lot of closet switches (i.e. 3560 or 2960) connected - you could those switches with one connection to each of your 4503. Then on loss of a core switch or ONE of the uplinks, you don't lose anything IF you have servers with multiple links, you could attach one to each 4503 if the server OS software supports that - exact method depends on the server OS. Low tech / non-automatic way would be to have spare ports on either, and you can move all non-redundant connections to the OTHER 4503 if one fails.