Hie Malcom,
Following link will help you in confguring the feature you want using IP SLA Monitor
http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_feature_guide09186a00801d2d74.html
This was previously known as RTR and now as IP SLA monitor
What we do is we configure an RTR like
rtr 1
type echo protocol ipIcmpEcho Target IP Address
timeout 2000
frequency 3
rtr schedule 1 start-time now life forever
By configuring above we are starting a ping to the target IP address with specified parameters like timeout and frequency.
We need to track the result of this rtr so we configure
track 100 rtr 1 reachability
Here you can also configure up and down notification times to ensure your route does not flap in case there is some flapping in WAN
Finally you can apply this tracked objects in your IP routes
ip route MPLS IP track 100
ip route DSL IP 150
Here first route is to MPLS IP (or whatever is your next hop to reach MPLS). In case track fails, it will return DOWN code. In such case this route will be removed from the routing table and next candidate which is the route to DSL will be installed