You can create a static ARP entry for a device that is not yet connected to the network or to prevent an entry from aging out.
device# configure terminal
device(config)# vrf test
device(config-vrf-test)# address-family ipv4 unicast
device(vrf-test-ipv4-unicast)# arp 10.6.6.7 0001.0001.0001 interface ethernet 0/1
device# configure terminal device(config)# vrf test device(config-vrf-test)# address-family ipv4 unicast device(vrf-test-ipv4-unicast)# arp 10.6.6.7 0001.0001.0001 interface ethernet 0/1