route outside 0.0.0.0 0.0.0.0 192.168.1.1 1
route outsidebackup 0.0.0.0 0.0.0.0 192.168.2.1 2

sla monitor 99
 type echo protocol ipIcmpEcho 8.8.8.8 interface outside
 num-packets 3
 frequency 10
!
sla monitor schedule 99 life forever start-time now
!
track 99 rtr 99 reachability
!
show run sla monitor
!
show run track
!
show sla monitor operational-state 99 | include operation
!
show sla monitor operational-state 99
!
route outside 0.0.0.0 0.0.0.0 x.x.x.x 1 track 99
route backup 0.0.0.0 0.0.0.0 y.y.y.y 254
!
object network isp1-nat
 subnet a.b.c.0 255.255.255.0
 nat (inside,outside) dynamic interface
!
object network isp2-nat
 subnet a.b.c.0 255.255.255.0
 nat (inside,backup) dynamic interface
!

router1:
interface gi0/0
 description outside
 ip address x.x.x.x x.x.x.x
 ip nat outside
 no shutdown
!
ip sla 99
 icmp-echo 8.8.8.8 source-interface GigabitEthernet0/0
 request-data-size 1
 tos 160
 timeout 2000
 threshold 2000
 frequency 15
 hours-of-statistics-kept 8
!
ip sla schedule 99 life forever start-time now
!
track 99 ip sla 99 reachability
 delay down 40
!
interface gi0/1
 description inside HSRP VIP: a.b.c.1
 ip address a.b.c.11 255.255.255.0
 standby 1 ip a.b.c.1
 standby 1 preempt
 standby 1 priority 105
 standby 1 track 99
 ip nat inside
!
ip access-list standard NAT
 permit a.b.c.0 0.0.0.255
!
ip nat inside source list NAT interface gi0/0 overload


router2:
interface gi0/0
 description outside
 ip address x.x.x.x x.x.x.x
 ip nat outside
 no shutdown
!
interface gi0/1
 description inside HSRP VIP: a.b.c.1
 ip address a.b.c.12 255.255.255.0
 standby 1 ip a.b.c.1
 ip nat inside
 no shutdown
!
ip access-list standard NAT
 permit a.b.c.0 0.0.0.255
!
ip nat inside source list NAT interface gi0/0 overload


ASA config:
route outside 0.0.0.0 0.0.0.0 a.b.c.1 1
!