Internet IP used for IP sla ICMP-Echo?

Hey all,

Just wondering what you guys used for an internet address for reachability for IP SLA? I'd assume 8.8.8.8 but don't know if they have a policy that blocks ICMP after a certain amount of time.

For detail, IP SLA nortbound primary circuit (Internet-bound), tracking on HSRP interface, priority drops of southbound interface if reachability is lost, traffic moves onto second switch + second circuit.

Thanks!