How Can i stop a transport request
SAP S D
looks like your question is not so clear. If you want to stop a transport request then dont send it in the first place.
But if you want to make a request as not transportable then save it as a local request. the other option is dont release the request from SE09 or SE10. It means request is created and has the ability to be transported but since its not released it cannot be transported.
Another option if you want to validate all the requests that are being transported, then you can setup a workflow. Now unless it is authorized by the concerned person the request cannot be transported.
I hope this answers your query.