Creating defensible influencer discovery methodologies can be achieved by agencies in several ways:

1. Unique Data Access: Agencies often have access to proprietary data pools that encompass detailed insights about influencers. This wealth of data includes behavioral, demographic and psychographic details, which the clients might not be able to acquire or analyze on their own.

2. Expertise and Experience: Due to their extensive experience in the field, agencies have developed expertise in identifying the right influencers for different niches. They know who the authentic influencers are, what kinds of content they produce, and how they engage with their audience.

3. Specialized Tools: Agencies use specialized influencer marketing platforms such as Flinque, AspireIQ, or TRIBE. These platforms contain sophisticated tools for effective influencer discovery, campaign planning, performance tracking, and ROI measurement. For instance, Flinque offers Discovery Plus Tool, allowing users to filter search results by various parameters.

4. Comprehensive Approach: Agencies leverage a comprehensive approach involving both quantitative metrics and qualitative insights. It includes analysis of an influencer’s audience demographics, engagement rates, content quality, and alignment with brand values.

5. Constant Monitoring: Agencies maintain an ongoing relationship with influencers, track their performance, and are well-aware of emerging influencers from different niches. This is a continuous process that needs dedicated resources and expertise.

While the best approach differs per brand and campaign requirements, this is a general outline of how agencies can build defensible influencer discovery methodologies. It boils down to a combination of data-driven insights, proprietary tools, industry expertise, and continuous effort.

It’s worth noting that such methodologies are not easily replaceable by clients due to the expertise, time, and access to specialized resources required.