My domain is pointing to main server and I'm using ns1 and ns2, what im wanting is that if my main server goes down for the domain to point to second server/backup server so the site remains online, is they some sort of way of doing this like backup name servers or something, so I can have my IP for main server as ns1.mydomain.com and ns2.mydomain.com but then have second IP on other name servers say ns3.mydomain.com and ns4.mydomain.com would that work or not and if not how else could I do this please?

Many Thanks
Louis

You could have your backup name server.
You could use a Domain name service and then put the service's Name server address as ns3 and ns4 on the domain that way when the site is down on NS1 & NS2 it will still show up. From the domain name services site.

These sites could help you.

zoneedit.com
xname.org
easydns.org

Example.com NS table
ns1.example.com ns2.example.com ns3.zoneedit.com ns4.zoneedit.com (It may be called different but you get my idea.)

Hope this helps!

I can add ns3 and ns4 on my domain manager, would I just point the IP address to my second server?
Or do i have to use one of them sites, xname.org is free so if I do it's ok but im not sure if I need to or not if I can add ns3 and ns4 in domain manager, doing it in my domain manager would it still do what I want it to, if main server goes down will it use ns3 and ns4 server?

Well i use domainz4less panel (Go daddy reseller)
You have to make 2 hosts on the desired domain you wish to use for name servers.

ns1.example.com (Main Server's IP)
and ns2.example.com (Second Servers IP)
ns3.example.com (Could be used for backup)
ns4.example.com (Again could be used for backup)

If you have a router you would use the routers IP for NS1 & NS2
You'll need to open up port 53 (DNS port) otherwise it wont work.

Then if your running bind on your server it will resolve the domain to point to your server here's a table of how this works.

Domain name->The name servers point the domain name to the IP-> The IP then sends the information to point it to the Server-> Domain is now accessible via web.

If you have a direct modem connection you would just add the computers IP to the domain manager.

Hope this helps.

I have my own servers so if you are using a Data center or a Hosting company then i would suggest asking them because settings could be different.

I can add ns3 and ns4 on my domain manager, would I just point the IP address to my second server?
Or do i have to use one of them sites, xname.org is free so if I do it's ok but im not sure if I need to or not if I can add ns3 and ns4 in domain manager, doing it in my domain manager would it still do what I want it to, if main server goes down will it use ns3 and ns4 server?

No, if you create several A records even if they are on different name servers, you will only end up with a round robin effect.
This would mean people would randomly hit your first and second server, and you can't control this.
To utilize your second content server you would need to create a proxy of some kind of forward your users to the right IP when the first server goes down.

use a 3rd party dns service like dnsmadeeasy, it offers load-balancing and/or failover, for a small price