Andrew raises a good point!
He's correct, another way (often the better way assuming you're not providing gateway redundancy) is not to have the Internet router on a internal host network. Whether you have the Internet router or the L3 switch as the default gateway, either, by default, will redirect hosts to the other router if that's where the traffic needs to go next (NB: BTW this is only an issue for hosts on the common network - non-common internal networks will use the "shared" internal host network for transit - i.e. redirects will not be an issue for them). If you do keep them using a shared internal host network, for which of the two routers to use as the host gateway, generally your L3 switch should be the gateway, as it usually has much more capacity than a WAN router (to support internal LAN-to-LAN traffic).
Another way to avoid the redirects is to disable them on the shared interfaces (mentioned, I believe, in the reference Andrew provided). This will then cause traffic to possibly transit a router that it really doesn't need to, but it avoids the hosts loading up redirected routes.
Although, if you do define a transit network, Andrew mentions using static routes, again, the two routing devices can share routing information via a routing protocol.
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PS:
If you want disable redirects, build a dedicated transit network, need additional help, etc., feel free to ask. I, and/or others, will try to help.
